To determine to measure of the unknown angle, be sure to use the total sum of 180°. If two angles are given, add them together and then subtract from 180°. If two angles are the same and unknown, subtract the known angle from 180° and then divide by 2.
Multiplication is basically repeated addition. So to convert repeated addition to multiplication, we take the number being added (7) and multiply it be the number of addens (5). Therefore, 7+7+7+7+7 = 5 • 7
