What’s the missing length? Or what is the hypotenuse?

Multiplying an even number of negative numbers gives an answer that is choose from:

Compare the subtraction problems 6/8 - 5/8 = 1/8 and 6/9 - 7/9 = 1/9 why is the answer to the first problem positive and the answer to the second problem negative

Which steps could be part of the process in algebraically solving the system of equations, y+5x=x^2+10 and y=4x-10