Question 14190
Let x = the number of students who paid $4.00 each to see "Our Town".
Since the club was able to reimburse the parents' $400.00 and still have $100.00 left, the club must have collected $500.00 ($400 + $100).  Now you can set up the equation to solve for x, the number of students.

x($4.00) = $500.00 Divide both sides by $4.00
x = 125 Students attended the play, assuming, of course that they all paid to enter.
Thornton Wilder would be gratified at the turn-out.