Newton's Second Law:

* F = ma

where:

* F = Force (in Newtons, N)

* m = Mass (in kilograms, kg)

* a = Acceleration (in meters per second squared, m/s²)

Given:

* Force (F) = 20 N

* Acceleration (a) = 4.0 m/s²

To find:

* Mass (m)

Solution:

1. Rearrange the formula to solve for mass:

m = F / a

2. Plug in the given values:

m = 20 N / 4.0 m/s²

3. Calculate the mass:

m = 5 kg

Therefore, the mass of the ball is 5 kilograms.