Question 587208
Let the ages of Tom and Alice be x and y respectively.

We know that Tom's age is thrice as Alice's age.
So,  x = 3y     --------------- (1)

Also, we know that the sum of their ages is 54.
Therefore, 
             x + y = 54
or          3y + y = 54   { Using equation (1) }
              4y = 54

           or   y = 54/4 = 13.5

Plugging back the value of y in equation (1), we get:
    x = 3*13.5 = 40.5

Hence, Tom's age is 40.5 years and Alice's age is 13.5 years

Hope this helps~!