Question: Replace an expression

1. how to replace in the expression:

the product of c * m * l by:

so that I get the following expression:





I have used subs and algsubs. And I have failed. I had to do it manually.
2. I obteniedo the following outputs of the units:
Unit(W),  Unit(s), Unit(degC)


I would like to display in format 2-D Math

3. In expressing the values of the parameters in their units and graph the function I get the following error
plot([Ca(t), Cb(t)], t = 0 .. 10, color = [red, blue], style = [point, line], useunits)
Warning, unable to evaluate the functions to numeric values in the region; see the plotting command's help page to ensure the calling sequence is correct
Some orientation
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