A small sphere of mass \(m = 2.0 \text{ kg}\) is released from rest at time \(t = 0\) in a viscous fluid. The sphere experiences a constant downward gravitational force and an upward drag force of magnitude \(F_d = bv\), where \(v\) is the speed of the sphere and \(b\) is a positive constant. The graph shows the speed \(v\) of the sphere as a function of time \(t\). Based on the graph, what is the value of the drag coefficient \(b\)?