Donny is measuring the angles of a triangle. he measures the first two angles and gets 30° and 100°. how could he find the measure of the third angle? a) subtract 100 and 30 from 180 since the three angles should sum up to 180°. b) subtract 100 and 30 from 360 since the three angles should sum up to 360°. c) add 100 and 30 since the third angle should be the sum of the first two angles. d) add 100 and 30 and then double it since the third angle should be twice the sum of the first two.