Answer:
230 were sold at the door
170 were sold in advance
Step-by-step explanation:
x=at door y=in advance
x+y=400
3x+2y=1030
y=-x+400
2y=-3x+1030
y=-3/2x+515
-x+400=-3/2x+515
x=230 y=170
Sarah has 12 quarters
