Answer:
There were 153 tickets sold at the door
Explanation:
Let a = number of advance tickets
d = number of door tickets
a+d = 631
a*3.50 + d*6 = 2591
Solving the first equation for a
a+d = 631
a = 631 -d
Substituting this into the second equation
a*3.50 + d*6 = 2591
(631 -d) *3.5 +6d = 2591
Distribute
2208.5 -3.5d +6d =2591
Combine terms
2208.5 +2.5d = 2591
subtract 2208.5 from each side
2208.5-2208.5 +2.5d = 2591-2208.5
2.5d = 382.5
Divide by 2.5 on each side
2.5d/2.5 =382.5/2.5
d = 153
There were 153 tickets sold at the door