Divide 7 into 42 your answer would be 6 then add 7 and get '13
It doesn't matter whether it's convex or not. The sum of the interior angles
of any 13-sided polygon is (11 x 180°) = 1,980°.
The answer you already have selected in the image is correct. Even eyeballing it, you can see that the smaller shape fits into the larger shape 4 times.