In general the area of a quadrilateral such as our TV screen is given by width multiplied by height. In this case we know that width = height + 18, so we can say that the area = height x (height + 18).
The distributive property allows us to multiply a sum, in this case (height + 18) by multiplying each addend and then adding the products. So, using the distributive property we can simplify the expression so that: area = height^2 + (18 x height)
