A car is traveling at 20 meters per second. The driver steps on the brake. The car is in equilibrium
equilibrium means that all forces acting on the object are balanced / cancel each other out. it can also mean that the object is not accelerating. thus, an object can be in equilibrium whether it is motion or not, as long as forces are balanced.
since it's said that it braked, the car is at rest, and thus it is in static equilibrium.
hope this helps~ :)