A bicycle store costs ​$1800 per month to operate. The store pays an average of ​$55 per bike. The average selling price of each bicycle is ​$75. How many bicycles must the store sell each month to break​ even?

Let x be the number of bicycles the store must sell each month to break even.

The total cost of operating the store is $1800 + $55x.
The total revenue from selling the bicycles is $75x.
At the break-even point, the total cost equals the total revenue, so:
1800 + 55x = 75x
20x = 1800
x = <<90=90>>90
The store must sell 90 bicycles each month to break even. Answer: \boxed{90}.