math word problem

Question

The employees from maintenance go for coffee together every day at 9 a.m. On​ Monday, Hector paid

​$5.70 for three cartons of​ milk, three cups of​ coffee, and seven doughnuts. On​ Tuesday, Guillermo paid ​$7.00 for four milks, four ​coffees, and eight doughnuts. On​ Wednesday, Anna paid ​$5.45 for two ​milks, five ​coffees, and six doughnuts. On​ Thursday, Alphonse had to pay for three ​milks, five ​coffees, and eight doughnuts. How much change did he get back from his ​$10 bill?

Answer 1

570=3M+3C+7D

700=4M+4C+8D

545=2M+5C+6D

? =3M+5C+8D

Multiply 1st by 4/3

subtract 2nd from 1st to get 60=4/3 D or D =(3/4)60=45 cents for a donut

plug that into the 2nd & 3rd equations to get

700-360=340=4M+4C

545-270=275=2M+5C Now double that to get

550=4M+10C Now subtract

340=4M+4C to get

210 =6C or C =210/6= 35 cents for coffee

340=4M+4(35)

4M=340-140=200

M=200/4=50 cents for milk

M=50, C=35, D=45

3M+5C+8D=150+165+360=675

1000-685=$3.15 change from $10 bill