Find the smallest number of flowers that can be put in vases in groups of 6 and 9?

The correct option is C 18
The smallest number of flowers that can be put in vases in groups of 6 and 9 is nothing but the smallest number that is divisible by 6 and 9 both.

We need to find the L.C.M of 6 & 9.

$\begin{array}{cc}3& 6,9\\ 2& 2,3\\ 3& 1,3\\ & 1,1\end{array}$

L.C.M = 3 × 2 × 3 = 18