A $166$-lb skydiver jumps out of an airplane (with zero initial velocity). Assume that $k = 0.7$ lb-s/ft with a closed parachute and $k = 4.7$ lb-s/ft with an open parachute. What is the skydiver's velocity at $t = 25$ s if the parachute opens after $20$ s of free fall?

velocity = ft/s