Which species is the pioneer species?

16.3 N

Explanation:

The net force acting on an object is essentially the sum of all its vector forces.

Here, one force is of the ball rolling. Because the force is in the same direction as where the ball is rolling, we will denote it as positive 20 N.

The second force is the force of friction. Friction is the force pushing against an object, so it's moving in the opposite direction as the ball. Hence, we denote that as negative 3.7 N.

Adding these, we get:

20 + (-3.7) = 16.3 N