Loosely, "varies inversely" means that as one quantity increases, the other decreases. Specifically, if x and y vary inversely, then y = k/x where k is some constant (a particular number).
Another way to write that relationship is xy = k. To find the value of k for this problem, you need a numbers for x and y that go together.
Suppose x = number of children and y = number of candies (it doesn't matter what order these go in as long as you keep track!).
"When 12 children are present, 140 pieces of candy are consumed." So when x = 12, the value of y = 140.
xy = k
(12)(140) = k
1680 = k
Now, when x = 8 children,
8y = 1680
y = 210
