Final answer:
The base area of Box 3 is x^2 + 4x.
Step-by-step explanation:
The base area of Box 3 can be found by multiplying the length and width. From the given information, we have:
Length = 4 + x
Width = x
To find the base area, we can substitute the values of length and width into the formula:
Base area = (4 + x) * x
Simplifying the expression, we get:
Base area = 4x + x^2
So, the base area of Box 3 can be represented as x^2 + 4x.