-10x + 2y = 4
add 10x to both sides (we do that because it cancels the negative 10x out)
2y = 4 + 10x
divide everything by two (because we need to get y alone on one side)
y = 2 + 5x
flip the 5x and 2 (because that is the form of y intercept form)
y = 5x + 2
