Find the 8^th term of a G.P., if its common ratio is 2 and 10^th term is 768.

In a G.P., the 4^th term is 48 and 7^th term is 384. Find its 6^th term.

Rohit writes a letter to four of his friends. He asks each one of them to copy the letter and mail to four different persons with the instructions that they move the chain similarly. Assuming that the chain is not broken and that it costs ₹ 10 to mail one letter, determine the amount spent on postage when the fourth set of letters is mailed.