The number of candies consumed varies inversely with the number of children present. when 12 children are present,140 pieces of candy are consumed. therefore, when 8 children are of candy are consumed

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