If a plant grows 15 inches a month how many months does it take for the plant to grow 66 inches tall?

Question

It takes a plant 1 month to grow 15 inches and 6 months to grow 30 inches. How many months will it take the plant to grow 66 inches?

Answer 1

15= x + m

30 = x +6m

96 = 6x +6m subtract 2nd equation to get

66 = 5x

x = 66/5 = 13.2 inches = initial height

m = 2.8 inches growth per month

h = 13.2 +2.8m = 66

2.8m = 66 -13.2 = 52.8

m = 528/28 = about 18.86 months to grow to 66 inches