Explanation:
the answer is the factor of n : 70.
with every sold ticket the charity raises $70.
add on :
to break even (to have at least 0 or more dollars as profit) they need to sell at least
70n - 1500 = 0
70n = 1500
7n = 150
n = 150/7 = 21.42857143...
that means, since they can't sell parts of tickets, they need to sell at least 22 tickets.