Firstly, calculating the cost price of the 600 quintals of rice:

Cost price of 1 quintal of rice = Rs 250

Therefore, the cost price of 600 quintals of rice = Rs 250 x 600 = Rs 1,50,000

Then calculating the total profit the grain merchant made:

Profit = 7% of cost price

therefore 7/100 x Rs 1,50,000 = Rs 10,500

To find the selling price of 600 quintals of rice, we need to add the profit and overhead charges to the cost price:

Selling price = cost price + profit + overhead charges

Overhead charges = Rs 1000

therefore the selling price would be Rs 1,50,000 + Rs 10,500 + Rs 1000 = Rs 1,61,500

Therefore, the total profit made by the grain merchant is Rs 10,500 and the selling price of 600 quintals of rice is Rs 1,61,500.