Six counters are 1/3 of the set. How many counters are in the whole set?

So it says 6 counters are 1/3 of the set.

6 = x/3 (x represents the whole set)

Multiply both sides by 3.

(6 * 3) = (x/3) * 3

18 = x

Since x represents the whole set, we can say that 18 counters are in the whole set.