This is how to solve the problem:
We know that the growth rate is constant for both species of plants. So we can say that the height is a linear function of the number of days since d = 0.
Assumption (1 month = 30 days)
Species A:
Growth rate = 2 cm/month = 2/30 = 1/15 cm/day
Height on day d = 0: 12 cm
Height: H(d) = 12 + d/15
Species B:
Growth rate = 3 cm/month = 3/30 = 1/10 cm/day
Height on day d = 0: 10 cm
Height: H(d) = 10 + d/10
The answer to your question Is letter B
