Have you tried to do this yourself first?
Evaluate the expression for the given value of the variable(s). 5a + 5b; a = -6, b = -5?
This is not really a question about finding a solution. It is about evaluating (determining) the value of 5a + 5b when a = -6 & b = -5
To do that, just substitute -6 for a, -5 for b and add the resulting products together. In this case, the evaluation is the solution and it is also a unique solution.
-55
42, but the real answer is in your math book.