The average rate of hair growth is 2 and 1/2 cm every 2 months

At that rate how many months will it take to grow 22 and 1/2 cm of hair

It would take a total of 18 months to grow 22 and 1/2 cm of hair. This can be calculated by dividing 22.5 cm by 2.5 cm (the rate of growth every 2 months) which equals 9. Then multiplying 9 by 2 (since each cycle of 2 months) = 18 months.