For the first plan:
Joining fee = $150
monthly fee = $10
Cumulative cost in x months = $(150 + 10x)
For second plan:
Joining fee = $50
monthly fee = $30
Cumulative cost in x months = $(50 + 30x)
Let the cumulative costs of both plan are equal after x months.

On 5th month, the cumulative costs will be equal.
Cost = 50 + 5Ă—30 = 50 + 150 = $200