for 4. multiply our y and dx to the other sides. From there integrate and you should be able to get your answer ... it should come out to something like the equation of a circle (or something similar)
For Q5 envision that you are working to find the volume of a cone and that the axis you are rotating around is the height multiplied by the pronumeral squared which serves as the radius multiplied by pi.
for 5. take out 4 as a factor ... leaving with 2 x sqrt(4-x^2) ... then you're left with something like 2 int of sqrt(2^2-x^2) ... from that, you can use the standard volume of a circle = 4/3 x pi x r^3 where r =2.