Answer:
A) 
B)
Step-by-step explanation:
A)Let's call the height of the plant
and this height will be 6 inches on the day 0 like this:

on the day 1 of the month the plant will have the original 6 inches plus the height it grew the first day which will be 1.5 inches

on the day 2 of the month the plant will have the original 6 inches plus the height it grew the first day plus the height it grew the second day which will be again 1.5 inches

we can see that on the day 1 we add 1.5 inches one time, on the day 2 we add 1.5 inches two times. it is possible to say now that the height will be the original 6 inches plus 1.5 times the days of the month like this:

We will solve for x because we need to find the number of days for a given h like this:

and this will be our equation that trent can use to find the number of days (x), it will take the sunflower to a given height.
B)to know how many days it will take for he sonflower to grow to a height of 45 inches we replace h in the equation with 45 like this:

The sunflower will take 26 days to grow to a height of 45 inches