You're looking for the number 13 and 7 can go into.
You can use the listing method.
13: 13, 26, 39... and so on, and so on.
7: 7, 14, 21, 28, 35, 42, 49.... and so on.
An easier way to do it is to simply multiply 13 by 7.
\(13*7= 91\)
13 and 7 can go into 91, evenly.
Hope this helped!
