Answer:

Step-by-step explanation:
so basically make a system of equations using what's given and solve.
Understand that the equation is the same as 
First: make two points to plug in
(0, 150) and (1, 450)
Therefore x (or t) is the time in months
and y (or N) is the number of lilies
Second: Plug in to make system

Third: solve
let's start with the fist equation
first simplify: b to the zero power is just 1 

Now plug in 150 to the a in the other equation

solve for b
simplify: 

b=3
now you're done
equation: 