Given:
12 inches in 1 foot
number of inches in 2.5 feet
2.5 feet * 12 inches/1foot = 2.5 * 12 inches = 30 inches
1 foot + 1 foot + 0.5 foot = 2.5 feet
12 inches + 12 inches + 6 inches = 30 inches
12 inches : 1 foot = x : 2.5 feet
12 inches * 2.5 feet = x*1foot
30 inches * feet = x * foot
30 inches = x