math help please?

Question

12: What is the surface area of a rectangular prism with these dimensions: 2" x 10" x 16"
424 sq in
3840 in
320 sq in
26 2/3 in


14: Name the solid for which the equation: V = bh can be used.
Sphere
Prism
Cone
Cylinder


15: Name the solid for which the equation: V = 1/3(pi)r2h, can be used.
Sphere
Rectangular Prism
Cone
Cylinder


16: Name the solid for which the equation: L = 2(pi)rh can be used.
Sphere
Rectangular Prism
Cone
Cylinder


17: A cylindrical tank is 12' in diameter and 15' high. How many cubic inches does it contain?
2015.5 cu. in
1856 cu.in
1774.7 cu. in
1695.6 cu. in


18: Find the weight of a steel block 6" x 4" x 8" if one cubic foot of steel weighs 480 pounds.
56 7/9 lb.
53 1/3 lb.
50 1/2 lb.
49 2/3 lb.

Answer 1

12: A rectangular prism has 6 surfaces:
2 at 2*10
2 at 2*16
2 at 10*16

So 2*2*10 + 2*2*16 + 2*10*16
=424

14 Volume = base * height
can only work if the cross sectional area stays the same over the height of the object.

So cylinder

15 V=1/3*PI*r^2*h

Is the volume of a cone.

16 Cone

17 Volume of a cylinder is pi*r^2 (Area of the base) *h
so r=d/2 = 6 so we get:
V=3.14*6^2*15
V=3.14*36*15 = 3.14*540
540*3 = 1620, so the answer will be a bit larger but close to that.
1695.6

18 Volume in cu ft is
6/12 * 4/12 * 8/12 = 1/2 * 1/3 * 2/3
=2/18 = 1/9

so if 1 cu ft = 480 lbs, 1/9 cu ft = 480/9 lbs
=53.3

Answer 2

12. 26 2/3
14. Cone
15. Cylinder
16. Sphere
17. 1696.6
18. 7/9