geometry

Use proportions. They look like this ---> \(a/b=c/d\)

ABC ~ XYZ AB=3 XY=12 BC=4 YZ=?

AB/BC = XY/YZ     so

3/4  = 12/YZ     cross-multiply

3 YZ  = 4 * 12

3 YZ  = 48    divide both sides by 3

YZ =  16