chapter 12 - income tax - example 12.4

In this example on page 8, while deducting the tax annuity to arrive at the price given, we multiply the tax annuity by v^4/12.
I understand that tax payments are due 4 months after each coupon is received, but could someone explain how multiplying the tax annuity by v^4/12 leads to that?

 

= v^(4/12) means (1/(1+i))^(4/12).

The tax on 6 Pounds need to be paid after 4 months.

to match the timing of the income and tax we are discounting tax by 4 months,

then we are discounting entre thing to time Zero.