How much was the cost of each?

Question

On​ Monday, Harold picked up six donuts and four large coffees for the office staff. He paid $6.70. On​ Tuesday, Melinda picked up four donuts and six large coffees for the office staff. She paid $7.00. What is the cost of one​ donut? What is the cost of one large​ coffee?

Answer 1

d= cost of donuts

c=cost of large coffee

6d+4c = 6.70 --------eq 1

4d+6c =7.0 --------eq 2

solve these 2 equation simultaneously to find value of c and d

multiply eq 1 with -4 and eq 2 with 6

-24d -16c = -26.8

24d +36c =42

add these 2 equations

20c =15.2

c= 0.76

substitute value of c in equation 1

6d+4c = 6.70

6d+4(0.76) =6.70

6d + 3.04 =6.70

6d =3.66

d =0.61

d= cost of donuts=$0.61

c=cost of large coffee=$0.76