Remark When you have two parallel lines cutting the sides of a triangle and one of them is the base of the triangle, then the 2 sides cut form a proportion. The safest way to handle this is to set up the proportion so that you are talking about sides of similar triangles..
Givens BD || AE CD = 16 CE = 16 + 4 CB = 12 CA = 12 + x
Set Up the Proportion CD/CE = CB / CA
Substitute and Solve 16/20 = 12/(12 + x) Cross multiply 16*(12 + x) = 20 * 12 Combine the right 16*(12 + x) = 240 Remove the brackets. 192 + 16x = 240 Subtract 192 from both sides. 16x = 240 - 192 16x = 48 Divide by 16 x = 48 / 16 x = 3
