how to compute federal withholding tax using percentage. I keep getting stuck on step 6 9 See Below)

1.	Total wage payment		$800.00
2.	One allowance	$77.90
3.	Allowances claimed on Form W-4	2
4.	Multiply line 2 by line 3		$155.80
5	Amount subject to withholding (subtract line 4 from line 1)		$644.20
6.	Tax to be withheld on $644.20 from Table 1single person, Table Link		$81.23

Explanation for step 6:

Go to Table 1 (a) Single Person

$644.20 is OVER $222 BUT NOT OVER $767 so to compute amount to withhold

$17.90 plus $15% of Excess over $222

Computation: $17.90 + 15% (644.20-222) = $17.90 + 63.33 = $81.23