The state governments are able to focus entirely on the citizens that live there. The federal government has to deal with wide spread, national issues, and would not provide the care and attention that the smaller state governments can.
You can buy 4 shirts because you bought one pair of jean (80 - 29 = 51) and so with the leftover money you could buy 4 shirts because (12 x 4 = 48) and then you'd have a leftover 3 dollars.
