Explanation
To find the total price, multiply the number of standard mattresses by the price of a standard mattress, and the number of deluxe mattresses by the price of a deluxe mattress. There were 12 standards at 100 dollars each, so that's 12(100). There were seven deluxes at 160 dollars each, so that's 7(160). Altogether that's 12(100) + 7(160).