Question 398824
Let {{{n}}} = the number of times in a month the 
bridge is crossed.
Let {{{C}}} = monthly cost
With pass:
{{{C = 30 + 3.5n}}}
without pass:
{{{C = 5n}}}
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{{{30 + 3.5n = 5n}}}
{{{1.5n = 30}}}
{{{n = 20}}}
The bridge must be crossed 20 times to make 
the monthly costs equal