* Know the conversion: There are 12 inches in every foot.

* Calculate for the whole feet: 3 feet * 12 inches/foot = 36 inches

* Calculate for the half foot: 0.5 feet * 12 inches/foot = 6 inches

* Add the two parts: 36 inches + 6 inches = 42 inches

Answer: There are 42 inches in three and a half feet.