On Monday, Archie paid $3.40 for three doughnuts and two coffees. On Tuesday he paid $3.60 for two doughnuts and three coffees. On Wednesday he was tired of paying the tab and went out for coffee by himself. What was his bill for one doughnut and one coffee
3d + 2c = 340 -- times 3 --> 9d + 6c = 1020
2d + 3c = 360 -- times 2 --> 4d + 6c = 720
subtract them....
5d = 300
d = 60
back into the first
180 + 2c = 340
2c = 160
c = 80
coffee costs 80 cents, doughnuts cost 60 cents
so a coffee and a doughnut will cost him $1.40
(time to have your textbook updated)