Solution
= Solution
The magnetic superpotential $W\sim qMq$ must have <R-charge> two, so
$$
R[M]=2-2R[q]=2\left(1-\frac{N_c+1}{N_f}\right).
$$
Therefore
$$
\boxed{\Delta(M)=\frac32R[M]
=3\left(1-\frac{N_c+1}{N_f}\right)},
$$
exactly matching the R-charge and dimension of the electric meson $\Phi^i\Phi^j$.