The boy on the bus gave a thumbs up to the kid swimming because of his t-shirt.
Nobody (Have written) to me since my brithday.
Because the context of what your speaking about is already given. Your just putting it into your own words.
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