Computation of Operating ROA:

ROE = ((ROA + (ROA - Interest Rate)*(Debt/Equity))*(1-Tax Rate)

3% = ((ROA +(ROA - 6%)*0.5)*(1-20%)

3% = ((ROA + (0.5*ROA) - 0.03)*80%

3% / 80% = (ROA + (0.5*ROA) - 0.03

3.75% = 1.5 ROA - 0.03

3.75%+0.03 = 1.5 ROA

6.75% = 1.5 ROA

ROA = 4.50%

So, its Operating ROA is 4.50%. If you have any doubt you can ask me through comment box.