Answer:
the length of the magnet is 5cm
Explanation:
first convert the feet into inches: 2ft 6in=30in, 1ft 9in=21in
then convert inches into centimeters (times by 2.5): 30*2.5=75cm 21*2.5=52.5
then divide 52.5 by 3.5 to get a proportion: 52.5/3.5=15
then divide 75 by 15: 75/15=5cm