A rectangle has a perimeter of 78 cm. If a square has the same perimeter as the rectangle, the side length of the square is ___ cm.

If the rectangle and the square have the same perimeter, then the square must also have a perimeter of 78 cm. Because all sides in a square have equal length, the length of a side of the square is 78 ÷ 4 = 19.5 cm.