The known is
$100 install
6 months
$350.38 total
7% of bill in taxes
Unknown
monthly access fee = f
100 + 6( f + 0.07f ) = 350.38
100 + 6f + 0.42f = 350.38
100 + 6.42f = 350.38
- 100 - 100
-----------------------------
6.42f = 250
------- ------
6.42 6.42
f = $39 monthly cable fee