Question 366326
Let {{{d}}} = number of dances you need to attend to break even
Let {{{C}}} = cost for member and non-member
For member:
{{{C = 30 + 4d}}}
For non-member:
{{{C = 6d}}}
When are the costs the same?
{{{30 + 4d = 6d}}}
{{{2d = 30}}}
{{{d = 15}}}
When you attend 16 dances, the cost as a member 
is less than a non-member
check:
For 15 dances:
For member:
{{{C = 30 + 4*15}}}
{{{C = 90}}}
For non-member:
{{{C = 6*15}}}
{{{C = 90}}}
And for 16 dances:
For member:
{{{C = 30 + 4*16}}}
{{{C = 94}}}
For non-member:
{{{C = 6*16}}}
{{{C = 96}}}
OK