A parachutist whose mass is 90 kg drops from a helicopter hovering 1000m above the ground and falls toward the ground under the influence of gravity. Assume that the force due to air resistance is proportional to the velocity of the parachutist, with the proportionality constant b1 = 20 N-sec/m when the chute is closed and b2 = 100 N-sec/m when the chute is open. If the chute does not open until the velocity of the parachutist reaches 35 m/sec, after how many seconds will the parachutist reach the ground? Assume that the acceleration due to gravity is 9.81 m/sec^2.

The parachutist will reach the ground after __ seconds.