The size of interior angle=180-60=120°(angles at a point) The equation to calculate the total angle measure of a polygon is ((number of sides)-2)×180° Let x be the number of size (x-2)×180°=120x x-2=2x/3 3(x-2)=2x 3x-6=2x x=6 So the polygon has 6 sides and each interior angle is 120°