Two rock climbing gyms offer a two-month “trial period” training program. The first gym charges $4 per climbing session plus a one-time $50 fee. The second gym charges $6 per climbing session plus a one-time $30 fee. For what number of sessions is the cost of the program the same for each gym? Write a system of equations you can use to find at what number of sessions the cost of the trial period program at each of the gyms is exactly the same.