Word Problems; equations

[metalmachine]

Hey all! I have 2 problems I cant figure out. It basically comes down to finding the equation which I have been unsuccessful at. Here they are with the multiple choice answers.

1) A box with a square base and a volume of 1000 cubic inches is to be constructed. The material for the top of the box costs $4 per 100 square inches, and the material for the sides costs $2.25 per 100 square inches. If the side of the base must be at least 6 inches long, for what value of x will the cost of the box be $85?

33.37 in.
34.49 in.
32.05 in.
27.87 in.
28.91 in.


2) The top of a 9-ounce can of a drink is three times thicker than the sides and bottom (so that the flip-top opener will work correctly), and the can has a volume of 266 cubic centimeters. What should the radius and height of the can be in order to use the least amount possible of metal? [Assume that the entire can is made from a single sheet of metal, with three layers being used for the top]

r= 3.17 cm, h= 8.45 cm
r=2.77 cm, h= 11.06 cm
r=3.77 cm, h= 10.06 cm
r= 2 cm, h=21.17 cm
r= 1.38 cm, h=44.26 cm


Thanks guys

 

[stapel]

What have you tried? What variables have you defined? What expressions and/or equations have you created? How far have you gotten?

Please be complete. Thank you!

Eliz.