-3√45 + 3√20 = -3√(9 · 5) + 3√(4 · 5) =
= -3√(3² · 5) + 3√(2² · 5) =
= -3 · 3√5 + 3 · 2√5 =
= -9√5 + 6√5 = -3√5 ← the end
Answer:

Step-by-step explanation:
The function is given.

To find : 
The input for the function f(x) is (a + 1).
Replace x with (a + 1).

Expand brackets.

Simplifying.

If that was the end and the question was "How many boxes did she sell?" then the answer is 6 boxes.