Multiples of 4: 4,8,12,20,24,28,32,36,40. ..........

Multiples of 6: 6 12, 18, 24, 30, 36, 42, 48, 54, 60. .......

Least common multiple of 3,4,6: 12

1+ 12= 13

A: The three teachers met again in the library on February 13.