Solution
= Solution
The one-loop coefficient is
$$
b_0=\frac32\,2(N_c+1)-\frac12(2N_f)=3(N_c+1)-N_f.
$$
Thus asymptotic freedom is lost at
$$
\boxed{N_f=3(N_c+1)},
$$
and the theory is infrared free for larger $N_f$.
= Solution
The one-loop coefficient is
$$
b_0=\frac32\,2(N_c+1)-\frac12(2N_f)=3(N_c+1)-N_f.
$$
Thus asymptotic freedom is lost at
$$
\boxed{N_f=3(N_c+1)},
$$
and the theory is infrared free for larger $N_f$.