Find the value of x that makes DEF ~ XYZ.
DE / EF = XY / YZ
10 / 8 = ( x - 1) / 4
5/4 = ( x - 1) / 4 cross-multiply
4 * 5 = 4 ( x -1)
20 = 4x - 4
20 + 4 = 4x
24 = 4x
x = 24/4 = 6
