Well, hello.  If x = 60 degrees, y = 40 degrees, and those dashed lines are bisectors, what might we say is the value of z?

Quick review: to bisect something is to cut it into two equal parts. In this case, x is cut into 2 30-degree angles and y is cut into 2 20-degree angles. Are we there yet?

Z is equal to one of the bisected pieces of x + one of the bisected pieces of y, or 30 + 20 = 50.  Done and done!