a.
Given that;
each social dance has a $5 door fee.
Then for x social dances a model for the cost C (in $) is;

Cost equals the door fee per social dance multiplied by the number of social dance x.
b.
Given;
VIP membership at the studio costs $80.
So, the number of social dances required to save money to buy the VIP membership can be calculated by substituting C for $80 in the above model;

Therefore, the number of social dances required to save money to buy the VIP membership is 16;
