Anet force of magnitude 36n gives an object of mass m1 an acceleration of 6.0m/s2. the same net force gives m1 and another object of mass m2 fastened together an acceleration of 2.0 m/s2. what acceleration will m2 experience if the same net force acts on it alone?

In working toward the complete solution of this problem,
I'm going to use addition, subtraction, multiplication, and
division.  Also, I think I'll be using Newtons 2nd law of motion
like at least fifteen times, so I'll write it here for our review: 

                                 Force = (mass) x (acceleration).

-- When 36 N of force acts on m₁ it accelerates at 6 m/s² .

                                             36 N = (m₁) x (6 m/s²)

Divide each side by  6 m/s² :    m₁ = (36 N) / (6 m/s²) = 6 kg . 

-- The same force acting on (m₁+m₂) accelerates them at 2 m/s² .

                                             36 N = (6kg + m₂) x (2 m/s²)

Divide each side by  2 m/s² :    6kg + m₂ = (36N) / (2m/s²) = 18 kg

Subtract  6kg  from each side:            m₂ = 12 kg .

-- The same net force acts on  m₂  alone:

                                             36 N = (12 kg) x (acceleration)

Divide each side by  12 kg :    Acceleration = (36 N) / (12 kg) = 3 m/s² .