Atriangle has side lengths of 20 cm, 99 cm, and 108 cm. classify it as acute, obtuse, or right.

This doesn't make sense, as a triangle much equal 180, so it cannot have two angles bigger than 90, because this would mean it cannot be acute. A right triangle has one angle that is 90, obtuse as one that is bigger than 90 and two that are less, and an acute has three angles less than 90. Maybe there's a typo here? 

Because a triangle has to be 180 always that is considered an obtuse.