the average rate of hair growth is 2.5 centimeters every 2 months

at that rate, how many months will it take to grow 22.5 centimeters of hair

Based on the given rate, it takes 2 months to grow 2.5 centimeters of hair. Therefore, it would take 9 months to grow 22.5 centimeters of hair (2.5 centimeters x 9 = 22.5 centimeters).