I am trying to solve a simple two-equation linear system with solve, but I keep getting this weird result where the magnitude order of the numerator and denominator don't cancel out. Whenever I have a linear system with floating-point numbers, more unknowns than equations and try to solve it for a specific set of variables, this happens.

Any suggestions on how to get around this? Or do I need to solve it manually?

I bassically have one problem with an integral of the type:

and I want to change the integration variable. I've founded the IntegrationTools:-Change command, but it simply does not work.

givin the error:
Error, (in IntegrationTools:-Change) unable to determine new range for S

Any help is deeply appreciated.