Hey there! The equation for perimeter is 2L x 2W, or L + L + W + W.
If P is 50, and it's W is 10, then we can do 2(10) + 2L = 50. This, simplified, becomes 20 + 2L = 50. Subtract 20 on both sides, and you're left with 30.
The equation now becomes 2L = 30. Divide both sides by 2, and you're left with L = 15.
