Let 'x' be the age of Mrs. Belarmino's husband in March 2000 and 'y' be the age of their son in March 2000, than we have

x = 11 y

In March 2013 that is 13 years after March 2000 Mrs. Belarmino's husband will be x + 13 years old and their son will be y + 13. Now we have

x + 13 = 3 (y + 13)

By replacing x with 11 y in the last equation we have

11 y + 13 = 3 (y + 13)

11 y + 13 = 3 y + 39

11 y - 3y = 39 - 13

8 y = 26

y = 26 / 8

y = 3.25 years

y = 3 years and 3 months

Their son was 3 years and 3 months old in March 2000.