That is an error. I mean to write ₦2000 and not ₦20 000. Please pardon me for that error.
It there in the problem. I copied the the original words in the post i and put the concerned section in bold. You can see it below.
A man's income is N 180 000 per anum. He is allowed a tax-free income in the following: personal allowance N 72 000, child allowance N 4 500 for each child under 18 years for a maximum of 4 children, dependent relatives allowance to a maximum of N 18 000. Calculate the amount of tax the man will pay if has 5 children under 18 years and the taxable income is 10% for the first N 20 000, 15 % for over N 20 000 and up to N 40 000, 20% for over 40 000 and up to N 60 000, and 25% for over ₦60 000.
Have you seen it?