What's the runners acceleration with a mass of 80 kg?

It depends on the force

If force is f and acceleration is a then the equation would be

a = f/80 kg

The runner's acceleration depends on the net force acting on him.

His acceleration is going to be ...

(net force on him, in Newtons) divided by (80 kg).

The unit of the acceleration is meters/second-squared.

The direction of the acceleration is the same as the direction

of the net force.