Here we can use the formula

$$\begin{gathered} \text{Average (A)=}\frac{\mathrm{Sum} \mathrm{of} \mathrm{observations} \left(\mathrm{S}\right)}{\mathrm{No}. \mathrm{of} \mathrm{observations} \left(\mathrm{N}\right)} \\ \text{⇒ S=A×N} \end{gathered}$$

According to the question,

Sum of dresses 3 jute bags and a paper bag(A=60, N=4)

⇒S=60 X 4 =240

Later, the dresses of paper bag are eliminated, the average decreases by 10. (so A=50, N=3)

So, sum of dresses of 3 jute bags

⇒S=50 X 3 =150

Now,

The number of dresses in paper bag =(sum of dresses 3 jute bags and a paper bag)-(Sum of dresses 3 jute bags )

=240-150=90

Hence, Option D is correct.