z 2 - xy = __ where x=1/3, y= -2/5, and z= -5/6

$z^2-xy\\ =(-\frac{5}{6})^2 - (\frac{1}{3})(\frac{-2}{5})\\ =\frac{25}{36}+\frac{2}{15}\\ =\frac{125}{180}+\frac{24}{180}\\ =\frac{149}{180}$