2x + 2(x - 10) = 250 {perimeter is 2(width) + 2(length)}
2x + 2x - 20 = 250 {used distributive property}
4x - 20 = 250 {combined like terms}
4x = 270 {added 20 to each side}
x = 67.5 {divided each side by 4}
x - 10 = 57.5 {substituted 67.5, in for x, into x - 10}