Answer: D) 3x^2 + 15
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Explanation:
Draw a horizontal line to divide the rectangle into two parts (they don't necessarily have to be equal parts). Refer to the diagram below. The upper rectangle is x by 3x. So its area is length*width = x*3x = 3x^2
The lower rectangle is 5 by 3x, so its area is 5*3x = 15x
Combine those two sub-areas back together to get the overall area of 3x^2 + 15x
You could also use the distribution rule
3x*(x+5) = 3x*(x) + 3x*(5) = 3x^2 + 15x
