Answer:
There are 364,000 people in the Air Force.
Explanation:
Percentages
The N% of a number M is calculated by:

For example, 15% of 280 is

We know the total amount of people serving as of January is estimated to be 1,400,000 people and that 26% of them are serving in the Air Force.
Compute 26% of 1,400,000:

There are 364,000 people in the Air Force.