How do i find the greatest common factor? ?

factors of a number are those numbers that can divide the number exactly without leaving a reminder.

using 6 and 12 as an example

factors of 12 {1,2,3,4,6,12}

factors of 6 { 1,2,3,6}

then the common factor from both 6 and 12 are { 1,2,3,4,6}

and from this , the greatest common factor is 6.

i'm assuming it's looking for the missing length, which should be 4cm

hope this !