Answer:
You sold 15 cookies and 12 muffins
Step-by-step explanation:
So you're given that 1 cookie is sold for $3 and 1 muffin is sold for $7
You're also given that in total you made $129, and sold 27 items
Let's make equations from that, letting c stand for amount of cookies and m for amount of muffins.
Now we can use the second equation to find m:
c + m = 27
m = 27 - c
Not we can substitute m into the first equation to find c:
3c + 7m = 129
3c + 7(27-c) = 129 [substitute m for (27-c)]
3c + 189 -7c = 129 [distribute 7 into (27-c)]
-4c + 189 = 129 [combine like terms]
-4c = -60 [subtract 189 from both sides]
c = 15 [divide both sides by -4]
Now we can substitute c into the second equation to find m:
c + m = 27
15 + m = 27
m = 12
