Answer:
Let's define summer 1 as the year when Oliver planted the 4 plants.
At the end of summer 1 each plant produced 2 more plants, then now he has:
4*2 = 8 plants.
At the end of summer 2, this happens again:
Now he has
4*2*2 = 4*2^2 = 16 plants,
Then we can model the number of plants as a function of the number of summers.
P(s) = 4*2^(s)
s represents the number of summers that had been pass since the summer when he planted the initial 4 plants
When s = 0, we are in the first summer.
P(0) = 4*2^(0) = 4
So it is consistent.
Now we want to know the number of plants at the end of the fifth summer, this is:
P(5) = 4*2^5 = 128 plants.
And for the second question:
"how many strawberry plants will Oliver have in his garden given that there are an plants at the end of every n summers?"
Just replace s by n in the equation i wrote above:
P(n) = 4*2^n