We can draw the table for better understanding.
$\begin{array}{lll} & \textbf{S} & \textbf{M} \\ \text{Cost price:} & 90x & 100x \\ \text{Delivery charge:} & \text{₹ }150 & \text{₹ }0 \end{array}$
A person bought the items from the store $\text{S}$ and saved $\text{₹ }100$.
So, $90x + 150 = 100x – 100$
$\Rightarrow -10x = -250$
$\Rightarrow {\color{Blue}{\boxed{x = 25}}}$
$\therefore$ The price of the item at the online store $\text{S}$, if there are no other charges includes $ = 90x = 90 \times 25 = \text{₹ }2250.$
Correct Answer $:\text{B}$