In order for substitution to work, you need to solve for one variable. The easiest equation to use would be the bottom one for x.
x+4y=10
-4y -4y
_______
x= -4y+10
Then use the other equation, and plug in for x. So,
-10(-4y+10) - 10y= 20
So then you distribute to get: 40y-10y=20. From there you solve for y then plug into the original bottom equation to get x.
(x, y) will be your answer.
