= Solution
Normalize a fundamental cubic anomaly to $A(\mathbf{N_f})=1$ and its Dynkin index to $I(\mathbf{N_f})=1$. The two gauge colours give
$$
\mathcal A[SU(N_f)_L^3]=2,
\qquad
\mathcal A[SU(N_f)_L^2U(1)_V]=2.
$$
The left and charge-conjugated right fermions have opposite vector charges and equal multiplicities, so
$$
\mathcal A[U(1)_V^3]=0,
\qquad
\mathcal A[U(1)_V\text{-gravity}]=0.
$$
If the theory confined with unbroken chiral symmetry, gauge-invariant operators contain an even number of $SU(2)$ fundamentals and are bosonic, so no massless composite fermions could match the nonzero chiral anomalies. <'t Hooft anomaly matching> therefore forces chiral symmetry breaking, with its infrared Goldstone theory carrying the anomaly.
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