x=13 and z=112
you know that (13x-57) + (6x-10) = 180 since they are supplementary, so you will solve that. it will give you x=13. now that you know x, you can solve for z by plugging in 13 for x on 13(x)-57 since that and angle z are congruent. when you simplify, you will get z=112.
you can check your answer by doing (6x-10) +112=180. this is because they are supplementary. you should get x=13, and that is how you know you are right.