B is correct.
The risk-adjusted after-tax return on capital (RAROC) is computed by:

$$RAROC = \frac{\text{After-tax expected risk-adjusted net income}}{\text{Economic capital}} = \frac{ER + ROEC - IC - OC - EL - Taxes \pm Transfers}{\text{Economic capital}}$$

where,
Economic capital = JPY 4,200,000,000 × 0.10 = JPY 420,000,000
ER = expected revenue = JPY 4,200,000,000 × 0.032 = JPY 134,400,000
ROEC = pre-tax return on invested economic capital
= Economic capital × 0.014 = JPY 420,000,000 × 0.014 = JPY 5,880,000
IC = interest expense = JPY 4,200,000,000 × 0.004 = JPY 16,800,000
OC = Operating Cost = JPY 4,200,000,000 × 0.005 = JPY 21,000,000
EL = expected loss = JPY 4,200,000,000 × 0.02 = JPY 84,000,000

Taxes = (Revenue + Income − Interest − Operating Cost − Loss) × (Tax rate)
= (134,400,000 + 5,880,000 − 16,800,000 − 21,000,000 − 84,000,000) × 0.38
= (JPY 18,480,000) × 0.38 = JPY 7,022,400

Numerator (After-tax net income) = JPY 18,480,000 - JPY 7,022,400 = JPY 11,457,600. RAROC = JPY 11,457,600 / JPY 420,000,000 = 0.02728 ≈ 2.73%