Question

if you have a mass of 80 kg and your computer has a mass of 4 kg, and you are separated by a distance of 0.25 m, what is the gravitational force of the computer acting on you?

Answer 1

There are a pair of forces ... two of them ... between you and the computer. 
You're attracted to the computer, and the computer is attracted to you. 
The forces have equal strength.

  Force of gravity =  (6.67 x 10⁻¹¹ N-m²/kg²) M₁· M₂  / (distance)²

                             =  (6.67 x 10⁻¹¹ N-m²/kg²) (80 kg) (4 kg) / (0.25 m)²

                             =  (6.67 x 10⁻¹¹ x 80 x 4  N-m²)  /  (0.125 m²)

                             =      1.71 x 10⁻⁷  Newton

                             =    about  0.000 000 615  ounce .

THAT's why you don't feel especially attracted to your computer.

Answer 2

We know that:
F=G(Mm)/R²
All the units are in the SI, so we operate:
F=6,67*10⁻¹¹Nm²Kg⁻²((80kg)(4kg))/(0,25m)²
F=3,41*10⁻⁷N