Answer :
So movie club one:
Cost = 100+10n, where n is the number of movies
Club 2:
Cost = 15n
So when they are equal:
100 + 10n = 15n
100 = 5n
n = 100/5
n = 20
Cost = 100+10n, where n is the number of movies
Club 2:
Cost = 15n
So when they are equal:
100 + 10n = 15n
100 = 5n
n = 100/5
n = 20