Answers:
First row = 3
Second row = 12
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Step-by-step explanation:
Think of a square that has sides of 5 by 5. It's area will be 5*5 = 25. That means 25 is a perfect square.
We rule out 81 for similar reasons because 81 = 9*9
Also, 100 = 10*10 and 121 = 11*11
The only thing left is 3 which isn't a perfect square. We cannot multiply two of the same whole number to end up with an area of 3 square units.
Put another way,
is not a whole number while something like
is a whole number.
This is all for the first row.
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The second row is the same story.
4 = 2*2
9 = 3*3
144 = 12*12
36 = 6*6
This rules out everything but 12 in the second row. You can determine what is a perfect square through trial and error, or by memorizing what the perfect square numbers look like. With enough practice, they should be fairly memorized by some point.