A square has four right angles (90°). Each diagonal splits a corner into two angles of 45°. Note also that the diagonals cut each other in half at right angles. A rectangle has four right angles.

STEP 2 - Label the inside of the rectangle with the number that is being shared out (the first number in the calculation). STEP 5 - The array shows us that 12 can be split into 3 equal rows of 4.