Draw a model showing 2.4 divided by 3

12 years

Step-by-step explanation:

Represent the mother's age by m and the son's by 4.  Currently m = 36 years old.

In x years the mother will be three times as old as her son:

mother:  36 + x years old

son:  4 + x years old

The pertinent equation to solve is:

36 + x = 3(4 + x)

Performing the multiplication, we get:

36 + x = 12 + 3x, or

24 = 2x.  Then x = 12.

Check:  In 12 years, will the mother's age be 3 times the son's age?

Does 36 + 12 = 3(4 + 12)?

Does    48      = 48?  YES

The mother will be 3 times as old as her son in 12 years from now.