Answer
5x(4x+1)
Work Step by Step
First, we need to know that:
The area of wooden frame = outside area - side area
So, =(7x+1)(5x) - (5x)(3x)
We can now take 5x from both sides and put it outside =5x(7x+1-3x)
Simplify, =5x(4x+1)
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*Drawing the diagram helps us to understand the problem easier.