Which of the following is a composite number 13 39 91 139

Composite numbers are numbers that aren't prime. Prime numbers are numbers that have only 2 factors; 1 and itself. Composite numbers have more than 2 factors (2+ pairs).

13 = 1 • 13. 13 is prime, not composite.
39 = 1 • 39, 3 • 13. 39 is composite.

Although we've found our composite number, let's keep searching (just in case).
PENDING NUMBERS: 39.

91 = 1 • 91, 7 • 13. 91 is a composite number.
139 = 1 • 139. 139 is prime.

Your two composite numbers are 39 & 91.

I hope this helps!