The angle bisector divides the sides proportionally.
z/12 = 6/5 . . . . . . . . . write a proportion*
z = 12(6/5) = 72/5 . . . . . multiply by 12
z = 14.4
_____
* We consider the proportion easier to solve if the unknown is in the numerator. Then the solution is found by multiplying the equation by that denominator.
