Answer: The age of Mr. Lang's youngest son is 7 years old.
Step-by-step explanation:
Let's start by listing the factors of 84. The factors of 84 are 1, 2, 3, 4, 6, 7, 12, 14, 21, 28, 42 and 84.
We can only use numbers that are under 19 since we must add up to that total. Now we are left with 1, 2, 3, 4, 6, 7, 12, and 14,
1 can't be an option since 18 is not there to pair with it to add together for 19. For the same reason we can eliminate 2, 3, 4, 6, and 14.
Now we are left with 7 and 12. Let's see is they will work.
7+12=19
7×12=84
It works! Since 7 is the smaller number that's the age of Mr. Lang's youngest son.
