Take into account that the total area of the two rooms are:
A = 28 + 63 = 91
You can notice that the following expressions also result in 91:
7(4 + 9) = 7(13) = 91
7*4 + 7*9 = 28 + 63 = 91
Then, the answer is:
7(4 + 9)
7*4 + 7*9
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