smc

Let $a_n$ be the interior angle of the nth vertex, and let $b_n$ be the exterior angle of the nth vertex. From the conditions in the problem, $$a_n=7.5b_n$$ That means $$a_1+a_2\cdots a_n=7.5(b_1+b_2\cdots b_n)$$ Since the sum of the exterior angles of a polygon is $360^{\circ }$, the equation can be simplified as $$a_1+a_2\cdots a_n=7.5\cdot 360$$ $$a_1+a_2\cdots a_n=2700$$ The sum of the interior angles is $2700$ degrees. However, there is no other constraint on what angle the interior angles can be, so we can not for sure claim that the polygon is regular or not. Thus, the answer is $\boxed{S=2700^{\circ }\text{and}P\text{may or may not be regular}}$.