Answer: a. $14,000
b. $14,106
c. January 
2. $15,535
Explanation:
a. If Hank sends the bill in December. 
Tax rate is 30% this year. 
Amount is $20,000
After Tax Income = 20,000 * (1 - tax)
= 20,000 ( 1 - 30%)
= $14,000
b. If Hank pays Next year 
Tax rate is 33% 
After tax return rate of 12% 
Amount is 20,000
Tax = 20,000 * 33% 
= $6,600. 
Because this is next year, the present value of the tax needs to be computed for better comparison. 
With an after tax return of 12%, the PV will be,
= 6,600 * PV factor ( 12%, 1 period)
= 6,600 * 0.893
=  $5,894
The income therefore will be,
= $20,000 - 5,894
= $14,106 
c. Hank should pay in January as he would make more income. 
2. Tax rate is 25% next year and income is to be received next year. 
Tax = 20,000 * 25% 
= $5,000
PV of $5,000 = 5,000 * PV Factor (12%, 1 period) 
= 5,000 * 0.893 
= $4,465
After tax income = 20,000 - 4,465
= $15,535