I need help. I don't know why it can't find the variables.

You may notice that you get different result when you use different guess values.

Reason is that you don't provide five independent equations.

The two equations for qa and qb can be simplified so that these two values could be calculated directly without using a solve block:

But the remaining three equations are not independent. This means that you can derive one of them just by using the other two.

So there is one degree of freedom and an infinite number of solutions for A, L and T1.

Guess you will have to look for a fifth, independent equation.

Hi @MI_13148469 

I wanted to see if you got the help you needed.

If so, please mark the appropriate reply as the Accepted Solution. It will help other members who may have the same question.
Of course, if you have more to share on your issue, please pursue the conversation. 

Thanks,
Anurag