Given: Marked price of the toy = Rs. $770$. Discount = $10$%. Gain = $10$%.

Step-by-Step Calculation: Selling Price (SP) after discount: Discount = $10$% of $770 = 0.10 \times 770 =$ Rs. $77$. Selling price = Marked price - Discount = $770 - 77 =$ Rs. $693$.

Relation between Selling Price, Cost Price (CP), and Gain: Gain = $10$% of CP. SP = CP + Gain. So, $693 =$ CP $+ 0.10 \times$ CP.

Solving for CP: $693 = 1.10 \times$ CP. CP = $693 / 1.10 =$ Rs. $630$.