Answer:
The comparable tax rate is 3.95%, thus you should choose the 4.5% taxable account option.
Step-by-step explanation:
In order to convert the tax-free interest rate of 3% per year to the comparable taxable interest rate, one should consider that 3% is the interest rate after the marginal tax discount. If you are at the 24% marginal tax bracket, the comparable rate is:

The comparable tax rate is 3.95%, thus you should choose the 4.5% taxable account option.