The ratio of three angles of a triangle is 4 : 7 : 9.  What is the measure of the greatest angle?

9° 81° 63° 36°

81°

Sum of all three angles of a triangle = 180° ⇒ 4x + 7x + 9x = 180° ⇒ 20x = 180° ⇒ x = 9° ⇒  The greatest angle = 9x = 81°