On a Christmas package, Audrey needs to use only 40-cent stamps and 16-cent stamps. If she uses twice as many 40-cent stamps as 16-cent stamps, how many of each type of stamp must she use to mail a package costing $5.76 in postage?
number of 16 cent stamps --- x
number of 40 cent stamps ---- 2x
16x + 40(2x) = 576
96x = 576
x = 6
.... state your consclusion