according to the triangle sum theorem, all the angles in a triangle must add up to 180 degrees. if we know one angle is already 90, we do 180-90=90. the other 2 angles must add up to 90, exactly.
Huong is organizing paperback and hardback books for her club's used book sale. the number of paperbacks is 12 less than three times the number of hardbacks. huong had 162 paperbacks. how many hardback books were there?