Question

What is the solution to y=x+16 and y=-x+4??

Answer 1

y=x+16
y=-x+4

All you have to do is substitute. 
Put the second equation into the first equation.

-x + 4 = x + 16
4 = 2x + 16
-12 = 2x
-6 = x

Now substitute the x into one of the equations to get y.

y = (-6) + 16
y = 10

The solution to these equations is (-6, 10).