First, what was the total percentage of withholding and taxes?
6.2% + 1.45% + 12.8% = 20.45%
Second, what is 20.45% of 3360?
To answer this, you multiply the percent (as a decimal) by the value:
0.2045 x 3360 = 687.12
So 687.12 was withheld.
Third, what is 3360 - 687.12?
$2672.88
So here earnings - taxes = $2672.88