all angles around the center point V are 60° because when added together they equal 360°. the angles in a triangle always add up to be 180° and there is 1 right angle which is 90°. so first you subtract 90 from 180 leaving 90 over. then the angle right above it is 60 because it is part of that circle around point V. so you subtract 60 from 90 and what you have left over is the answer.
