To figure out the cost for 180 packages, you must first calculate how many packages they bought for $72. Since each case holds 12 packages, for $72, the company bought 24 packages (12×2). Then you have to divide 24 into 180 to figure out the cost for those 180 packages and get 7.5. To get the cost of the 180 packages, you must multiply 7.5 (the number of 24 packages that go into 180) by 72 (the cost of one group of 24 packages). You then get 540. The company must pay $540 for the 180 packages.