17.so if there are 2.54 cm in an inch that means that 1cm times 2.54=1 inchthere are 12 inches in a foot and 1 inch=2.54 centimter so 12 times 1 inch or 12 times 2.54=30.48 centimeters there are 3 feet in a yard so we take the previous measurements and multiply 30.48cm in a foot times 3 feet in a yard or 30.48 times 3=91.44 cm in a yard if you want to do it the long way, you can multiply 2.54 with 12 with 3 and get the same answer 91.44 cm in a yard
18. 2.50 / 2 = 1.25 not .80 It also looks like you are trying to divide the spaghetti boxes by the price, when it should be price by number of boxes.
19.unit cost is cost of 1 unit of a product, here its cost of 1 pound of sugar. In first case unit cost is $1.10.In second case cost of 2 pound = $1.98, or cost of 1 pound = [1.98/2] = $0.99. In third case cost 3 pound = $2.85, or cost of 1 pound = [2.85/3] = $0.95. We can see that as the quantity is increasing unit cost is decreasing.
Hope this helps!