Question 1025589
1.  {{{V = int(1, dV, 0,3) = int(pi*r^2, dx, 0,3) = pi*int((3x - x^2)^2, dx, 0,3) = pi*int((9x^2 - 6x^3 + x^4), dx, 0,3)}}}

==> The antiderivative is {{{3x^3-(3x^4)/2 + x^5/5}}}
==> The volume is {{{pi*(3*3^3 - (3/2)*3^4 + 3^5/5 )= (81pi)/10}}}

2.  {{{V = int(1, dV, 0,8) = int(pi*r^2, dy, 0,8) = pi*int((2-y^(1/3))^2, dy, 0,8) = pi*int((4 - 4*y^(1/3) + y^(2/3)), dy, 0,8)}}}

==> The antiderivative is {{{4y - 3y^(4/3) + (3/5)*y^(5/3)}}}
==> The volume is {{{pi*(4*8 - 3*8^(4/3) +(3/5)*8^(5/3))= (16pi)/5}}}


I leave the last one to you.