The statement of the problem is deficient; it is not possible to come up with a definitive answer.
Given the areas of the two squares, we know the side lengths of the two squares are 5*sqrt(3) and 3*sqrt(3).
The trouble is that "joined together" is not well defined. It makes sense to assume that part of one edge of one square is part of one edge of the other square; but that can happen in different ways that give different combined perimeters.
The other tutor showed the two squares joined like the following figure:
+----------+
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+ +------+
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+----------+------+
That tutor then showed how to find the combined perimeter by finding the length of each piece of the perimeter:
5*sqrt(3)+5*sqrt(3)+5*sqrt(3)+2*sqrt(3)+3*sqrt(3)+3*sqrt(3)+3*sqrt(3) = 26*sqrt(3)
Note that the calculation is easier by noting that the perimeter of the figure above is the same as the perimeter of this figure:
+----------+------+
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+ +------+
| | |
| | |
+----------+------+
The perimeter of that figure is simply
5*sqrt(3)+8*sqrt(3)+5*sqrt(3)+8*sqrt(3) = 26*sqrt(3)
And the perimeter of the combined figure is always 26*sqrt(3), AS LONG AS the edge of the smaller square does not extend past the edge of the larger square.
But the following figure -- in which the two squares are still "joined together" has a perimeter greater than 26*sqrt(3):
+----------+
| |
| |
| +------+
| | |
+----------+ |
+------+
So in order to come to a single answer to the problem, we need to make some assumptions -- and that makes the problem not well defined.