You need to ship a box across the country. The package delivery company you wish to use will accept a box for shipment only if the sum of the length...

You need to ship a box across the country. The package delivery company you wish to use will accept a box for shipment only if the sum of the length and girth (distance around) is at most 180 inches. Find the dimensions of the largest acceptable box with square front and back. (Let x be the measurement of one side of the square front. Let y be the length of the box.)