The two rectangles are similar. The shapes are the same but the sizes are different. The ratio of the smaller rectangle to the bigger one is constant.
Comparing the sides of the two rectangles, we would take ratio of the width of both rectangles and equate it to ratio of the lengths of both rectangles. It becomes
3/5 : 12 = x : 20
(3/5)/12 = x/20
3/5 × 1/12 = x/20
3/60 = x/20
Cross multiplying
60 × x = 20 × 3
60x = 60
x = 60/60 = 1
The enlargement is in a scale of 5. Multiplying any length on the smaller rectangle by 5 will give the corresponding length of the bigger
