Pablo is four yrs older than his sister. The product of their ages is 21. Determine their aged.

Let $F$ be Faith's age.
Let $N$ be Nabil's age.

"Nabil is four years older than his sister Faith":

"The product of their ages is 21":

Substitute $N = F + 4$ into $N \times F = 21$:

Factor the quadratic equation:

This gives two possible solutions for $F$:

Since age cannot be negative, Faith's age is $F = 3$ years.

Using the equation $N = F + 4$:

Nabil's age is 7 years.

Faith's age is 3 years and Nabil's age is 7 years.