I think the correct answer is C. i hope this helps
Answer:
230 were sold at the door
170 were sold in advance
Step-by-step explanation:
*i dont know if this is the proper way to do it but it has the correct answer
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
Add every side together then divide it by 100
You can multiply opposite sides, like so:
y*7 = 8*3
7y = 24
y = 24/7