Commission of sales on office equipment is paid at the rate of 12%. last week $2860 worth of office equipment was sold. what was the commission?

Can someone explain the elimination method to me for this problem?

An appliance store sells lamps at $95.00 for two. a department store sells similar lamps at 5 for $250.00. which store sells at a better rate

The volume of gas a balloon can hold varies directly as the cube of its radius. imagine a balloon with a radius of 3 inches can hold 81 cubic inches of gas. how many cubic inches of gas must be released to reduce the radius down to 2 inches?