An isosceles triangle has base angles that each measure 42°. Which equation can be used to find z, the measure of the third angle of this isosceles triangle in degrees?
84 + 2z = 180
84 + 2z = 180
42 + z = 180
42 + z = 180
84 + z = 180
84 + z = 180
42 + 2z = 180