What is his gross annual income?

There are 52 weeks in one year.

Gross annual income
= ($15.65 /h) × (36 h / week) × (52 weeks / year)
= $29296.80 /year

D is correct - simply multiply hourly rate by number of hours in a week and then by number of weeks in a year, assuming all holidays are paid.

15.65 dollars/hour * 36 hours/week * 52 weeks/year =>
15.65 * 36 * 52 dollars/year =>
5 * 3.13 * 36 * 52 =>
3.13 * 36 * 26 * 2 * 5 =>
3.13 * (31 + 5) * (31 - 5) * 10 =>
3.13 * (961 - 25) * 10 =>
3.13 * 936 * 10 =>
31.3 * 936 =>
313 * 936 / 10 =>
(300 + 13) * (900 + 36) / 10 =>
(270000 + 10800 + 11700 + 13 * 36) / 10 =>
(270000 + 22500 + (10 + 3) * (30 + 6)) / 10 =>
(292500 + 300 + 90 + 60 + 18) / 10 =>
29250 + 30 + 9 + 6 + 1.8 =>
29250 + 46.8 =>
29296.8

Looks right to me.