Question

I have a few questions! what is the gcf for

(21 and 54)
(55 and 90)
(16 and 30)
(42 and 91)
(66 and 121)

Answer 1

(21 and 54): 3

(55 and 90): 5

(16 and 30): 2

(42 and 91): 7

(66 and 121): 11

Explanation: