Let Fred's present age be denoted as $F$ and Mary's present age as $M$.

Step 1: Create equations based on the problem statement

• First condition: Fred is three times older than Mary. This gives us the equation: $F = 3M$

• Second condition: Four years ago, Fred was five times as old as Mary. This translates to: $F - 4 = 5(M - 4)$

Step 2: Solve the system of equations

Substitution method:

1. From the first equation, $F = 3M$, substitute this into the second equation: $3M - 4 = 5(M - 4)$
2. Simplify the second equation: $3M - 4 = 5M - 20$
3. Rearrange the terms: $3M - 5M = -20 + 4$ $-2M = -16$
4. Solve for ( M