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put this solution on YOUR website!(Please ignore all dotted lines [---] in the pictures. They are there so the picture would come out right.)
Suppose your original square has side length x:
_____
|-------|
|-------| x
|_____|
x (not to scale)
Then its area is

. Doubling the base gives the following shape:
__________
|-------------|
|-------------| x
|__________|
2x (not to scale)
Shrinking the height by 3 inches gives the following shape:
__________
|-------------| x-3
|__________|
2x (not to scale)
The area of this new rectangle is

.
This area is 40 square inches larger than the area of the original square.
Recall that the area of the original square is

.
This gives us the equation

.
Subtracting

from both sides gives

.
Then we subtract 40 from both sides to get

.
We can factor this into

, which means x = 10 or
x = -4.
Since x represents the length of the side of a square, x cannot be less than zero. Hence, x = 10 inches.