Final answer:
The federal income tax at 10% of the gross pay of $1287.50 is $128.75.
Step-by-step explanation:
The question requires us to calculate the federal income tax which is 10% of the gross pay. In this case, the gross pay is $1287.50. To find the federal income tax, we multiply the gross pay by 10% (or 0.10).
The calculation is as follows:
$1287.50 × 0.10 = $128.75
Therefore, the correct answer is b) $128.75.