V = ∫_0_^h^2π r(y)^2 dy

r(y) = r_b + m y

m = (r_t - r_b) / h

V = ∫_0_^h^ 2π ( r_b^2 2 + m y + m^2 y^2 ) dh

V = 2π r_b^2 y + m y^2 / 2 + m^2 y^3 / 3 ) |_0^h

V = 2π h ( r_b + m h / 2 + m^2 h^2 /3 )

V = π h ( r_b + r_t + 2 (r_t^2 - 2 r_t r_b + r_b^2) / 3)