z=56°
explanation: since the one angle is 90°, you need to take 68 away from 90, you get 22. then since the line between angle 78° and y, would add up to 120°, you must take 78° away from 120°, giving you 42 for angle y. now for 3-sided triangles, their 3 angles add up to 120°, so add 42 and 22, you get 64, and finally take 64 away from 120 and you get angle z, which is 56°
