Question: Error using subs command

I wrote the following lines in MAPLE:

The program is to find the three constants a, b and c using the three boundary conditions. Maple correctly evaluated the three constants but instead of T_w and T_inf it is showing the final result in the form (a+b*y+c*y^2)_w and (a+b*y+c*y^2)_inf i.e. it is not recognizing T_w and T_inf as constants.Moreover when I substitute the values of a, b and c back in the expression for T using subs command I get an error message. I cannot get the

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