Answer:
Size of each group = 
Step-by-step explanation:
Total number of paint brushes = x
Since each the three groups are equally sized, to get the number of paintbrushes in a group, we will have to divide the total number of paint brushes by 3
∴ We have, number of paint brushes in a group = 
= 
this is also the same thing as saying
×
This shows that the size of the new group is the same as
the size of the original group
You use a system of equations
x= coffee
y= donuts
x+y=100
3x+y=180
there’s 3 ways to solve system of equations substitution graphing and elimination. it would be easiest to use substitution here. So you multiply x+y=100 by -1 so it become -x-y=-100. then you combine it with the other equation and get 2x=80 so x=40 which means 40 cups of coffee were sold then you plug it back in to find y. 40+y=100. y=60.
y= 60 (donuts). x= 40 (coffee)