A certain force gives a mass m1 acceleration 12.0m/s2 the same froce gives an accerleration of 9.0m/s2 when mass m1 and m2 are tied together what accleration would this froce give m2 if m1 is untied from m2 ?

Hint: you have

F=m_1 \times 12\frac m{s^2} = (m_1+m_2)9\frac m {s^2}.

So you can express m_2 in terms of m_1. Then:

a_2 = \frac F {m_2} = \frac {m_1 \times 12\frac m{s^2}}{m_2}.

Post back with what you get for an answer and we'll check it for you.