@Preben Alsholm showed some syntax corrections.
Beyond that, I would also point out that you are mixing exact quantities such as Pi and 3/4, with fixed point quanties such as 0.1 and 0.19, with floating point calculations such as y^1.5 . The fact you are using solve() means you want an exact solution, but the 0.1 and y^1.5 and so on "contaminate" the solution finding making an exact solution difficult. When you have this kind of contamination, solve() is often unable to find answers, and the answers it does find not infrequently fail back-substitution and are sometimes spurious (e.g., finding a real root of an equation that provably has no real roots.)
In the matter of y^0.5 and x^2.5 and so on: in Maple, when there is a fixed point or floating point power in an exponentiation, rather than a rational power such as 1/2 or 5/2, then the operation is defined in terms of the "principle root", y^n evaluating to exp(n * ln(y)) , and the operation is defined as taking place in floating point (and so subject to the Digits limitations.)
Try this experiment:
cu := r->r^3.0: curr := r->r^evalf(1/3): c := r->cu(curr(r))-r: plot(c,0..1);plot(c,0..100000);c(100000);
In the first plot you will see random noise both negative and positive; in the second you will see that the trend is more and more negative and that the range of the noise gets greater and greater. By 100000 the discrepancy has grown to -0.00010 .
If you try the same plot with rational exponents, the output will look similiar, because plot() is going to be sending floating point numbers into the calculations. But any one rational point you evaluate at such as 100000 will have 0 discrepency. For finding exact solutions, you can't have any discrepency.
Thus, if you want to use solve() because you want exact solutions, you should change all of the literal numeric constants to rational numbers, leaving the named constants such as Pi unchanged. Or you should switch to using fsolve() instead of solve() -- and even if you do that, you should be giving some consideration to what you want expressions such as Pi + 0.1 to mean in your calculation.
When working with fixed-point constants or floating-point numbers, remember that Maple treats fixed-point constants as indicating that floating-point calculations may be used.
And always remember that floating-point calculations are non-associative and non-distributive, so if you are operating on them algebraically instead of procedurally, you are making a mistake of domain.
In the case above, switching to rational values and using solve() may take rather some time to complete. But whatever it does produce will be correct. If you can wait that long. Might be very long though...