The employees from maintenance go for coffee together every day at 9 a. m. On Monday, Hector paid $4.60 for three cartons of milk, three cups of coffee, and seven doughnuts. On Tuesday, Guillermo paid $8.30 for four milks, nine coffees, and eight doughnuts. On Wednesday, Anna paid $4.90 for two milks, five coffees, and six
doughnuts. On Thursday, Alphonse had to pay for five milks, two coffees, and eight doughnuts. How much change did he get back from his $10 bill?

The change will be $4.75

Step-by-step explanation:

Given data:

Monday

Total paid = 5.45

milk bought =3

coffee bought = 4

doughnuhts = 7

Tuesday

Total paid = 5.30

milk bought =4

coffee bought = 2

doughnuhts = 8

Wednesday

Total paid = 5.15

milk bought =2

coffee bought = 5

doughnuhts = 6

Thursday

Total paid = X

milk bought =5

coffee bought = 2

doughnuhts = 9

Let milk be m, Let coffee be c and Let doughnuts be d

3m + 4c + 7d = 5.45 (eqaution 1)

4m + 2c + 8d = 5.30 (equation 2)

2m + 5c + 6d = 5.15 (equation 3)

Using equation 1 and equation 2 ( to eliminate m)

3m + 4c + 7d = 5.45 (Multiply the whole equation by 4)

4m + 2c + 8d = 5.30 (Multiply the whole equation by 3)

12m + 16c +28d = 21.8

12m + 6c +24d = 15.9   (Subtracting the two equations)

0m +10c + 4d = 5.9

therefore 10c +4d = 5.9 (equation 4)

Using equation 2 and equation 3 (to eliminate m)

4m + 2c + 8d = 5.30 (Multiply the whole equation by 2)

2m + 5c + 6d = 5.15 (Multiply the whole equation by 4)

8m + 4c + 16d = 10.6

8m +20c +24d = 20.6  (Subtracting the two equations)

0m -16c -8d = -10

-16c -8d = -10 (equation 5)

Solving equation 4 and equation 5( to eliminate d)

10c +4d = 5.9 (Multiply whole equation by 8)

-16c -8d = -10 (Multiply whole equation by 4)

80c + 32d = 47.2

-64c  -32d = -40 (Adding the equations)

16c              =7.2

therefore c = 0.45

Substituting into equation 4

10(0.45) + 4d = 5.9

4.5 + 4d = 5.9

4d = 5.9-4.5

4d = 1.4

therefore d = 0.35

Substituting c and d into equation 1

3m + 4c + 7d = 5.45

3m + 4(0.45) + 7(0.35) = 5.45

3m + 1.8 + 2.45 = 5.45

3m = 5.45-2.45-1.8

3m = 1.2 therefore m = 0.4

Alphonse has to pay 3m + 2c + 9d

Alphonse change will be 10 - (3m + 2c + 9d) (Substituting m, c and d)

10- (3(0.4) + 2(0.45) + 9(0.35) = 10 -(1.2+0.9+3.15)

which simplifies to 10- 5.25=4.75

The change will be $4.75