F.3 maths question

It is pleased for me to solve your problem.

The salaries tax payable by Mr Lee is $3530. Find his net chargeable income.
let his net chargeable income be 40000+a
40000x2%+a x 7%=3530
0.07a=2730
a=39000
hence, his net chargeable income is $79000.

The net chargeable income ("NCI") depends on the year of assessment. The following calculations show the NCI for the Y/A from 2005/06 to 2011/12.

Y/A 2005/06
Since the tax exceed $3,000, the NCI falls within the 3rd level of progressive rate.
NCI = ($3,530 - $3,000) / 14% + $60,000
= $63,786

Y/A 2006/07
In this year, 50% of salary tax is exempted for payment. Thus the actual tax should be $7,060 ($3,530 / 50%). Since the tax exceed $6,600, the NCI falls within the final level of progressive rate.
NCI = ($7,060 - $6,600) / 19% + $90,000
= $92,421

Y/A 2007/08
In this year, 75% of salary tax is exempted for payment. Thus the actual tax should be $14,120 ($3,530 / 25%). Since the tax exceed $7,350, the NCI falls within the final level of progressive rate.
NCI = ($14,120 - $7,350) / 17% + $105,000
= $144,824

Y/A 2008/09
In this year, 100% of salary tax is exempted for payment, subject to a ceiling of $8,000. Thus the actual tax should be $11,530 ($3,530 + $8,000). Since the tax exceed $8,400, the NCI falls within the final level of progressive rate.
NCI = ($11,530 - $8,400) / 17% + $120,000
= $138,412

Y/A 2009/10
In this year, 75% of salary tax is exempted for payment, subject to a ceiling of $6,000. Thus the actual tax should be $9,530 ($3,530 + $6,000). (Note: 75% of $9,530 is $7,148 which is greater than $6,000, thus the maximum exemption is $6,000). Since the tax exceed $8,400, the NCI falls within the final level of progressive rate.
NCI = ($9,530 - $8,400) / 17% + $120,000
= $126,647

Y/A 2010/11
In this year, the data are identical to those in 2009/10; therefore the NCI is identical to that for 2009/10.
NCI = ($9,530 - $8,400) / 17% + $120,000
= $126,647

Y/A 2011/12
Since the tax exceed $800, the NCI falls within the 2nd level of progressive rate.
NCI = ($3,530 - $800) / 7% + $40,000
= $79,000