Answer: 0.1681 percentage point
Step-by-step explanation:
Here the stated interest rate = 8.145% = 0.08145
If the interest is calculated weekly,
In one year number of weeks= 52,
Thus, the effective interest rate in that case,

⇒ 
Now, If the interest is calculated semiannually,
In one year number of half years in one year = 2
Thus, the effective interest in that case,

⇒ 
Since, 
Thus, Tiffany's effective interest rate is 0.1681 percentage point greater when the interest is calculated compound weekly than when the interest is calculated compound weekly.