Yousaf, you need to compare how much John is going to pay under either alternative:
1) 3.2% simple interest rate. What John pays to borrow $500,000 for 3 years is equal to
$500,000*3.2%*3 = $48,000
2) 1.6% compound interest rate, compounded semi-annually.
Note that 1.6% is not the annual interest rate applied, but is already given to you as the compounded interest rate applied semi-annually. Otherwise it is clearly better to use option 2 as you pay half the interest rate than in option 1!
In this case, one pays interest rates every 6 months. More specifically, one pays 1.6% every 6 months. In a period of 3 years, there are 6 periods of 6 months each. So, John pays:
$500,000*[(1+1.6%)2*3 -1] = $49,961.45.
The conclusion is that John is better off paying a simple interest rate as it pays less over the assigned period of 3 years.