Can someone help me pls

Which equation represents a proportional relationship that has a constant of proportionality equal to 1/5

For f(x)=2x+1 and g(x)= x^2 -7, find (f•g)(x)

Find the measure of the interior angles of the following regular polygons: a triangle, a quadrilateral, a pentagon, an octagon, a decagon, a 30-gon, a 50-gon, and a 100-gon.