Change is the amount we get back after paying for the commodity.
Change = Money paid – The bill amount
Cost of the box of cereal = $3.98
Cost of Hamburger = $5.76
Cost of tomatoes = $2.87
Cost of milk = $4.46
Total cost of the four items = 3.98 + 5.76 + 2.87 + 4.46 =$17.07
Amount with Charlie = $20
Amount left with Charlie after paying $17.07
= 20 - 17.07
=20.00 - 17.07
=$2.93
So Charlie must expect to get back $2.93 as change.