Is it possible to have a polygon whose sum of interior angle is seven right angles?
No
Sum of interior angles =(2n−4)×90∘
=(2n−4)×90∘ = 7 x 90°
2n - 4 = 7
2n = 11
n=112
=5.5 (which is not a whole number)
As number of sides is not a whole number, it is not possible to have a polygon whose sum of interior angle is 7 right angles.