Isolate the x variable, changing the equation to 10x = 50 - y
We're not done yet, so divide the whole equation by 10 to get x by itself
x = 5 - y/10
If y = 50, then all you have to do is plug it into the equation we've just created!
x = 5 - (50/10)
x = 5 - 5
x = 0
