According to the question,

3 men can do a piece of work in 6 days. 5 Women can do the same work in 18 days

So, 3 × 6 = 5 × 15

⇒18 men = 90 women

⇒1 man = 5 women

 Here,

M₁= 5, D₁=18, W₂=1

M₂= 30-x, D₂= ?, W₁= 1

So as per the formula,

     M₁ D₁ W₂ = M₂ D₂ W₁

    $$\begin{gathered} \Rightarrow 5\times 18\times 1=30\times D_2\times 1 \\ D_2=\frac{5\times 18}{30}=3 days \end{gathered}$$

 Hence option A is correct.