If x-y=10 and x squared-y squared = 40 then y=?

12 I know I gave you the wrong answer

Solve for y in the first equation

-y=-x+10

y=x-10

Now substitute y in the second equation

x^2 - (x-10) ^2=40

x^2 - (x^2-20x+100) = 40

20x-100=40

20x=140

x=7

Plug the value of 7 in to any of the equations

7-y=10

y = (-3)

Final answer: y = - 3