Hamed own a local gold market that currently has XXXXXXXXXXsubscriber in Instagram at a quarterly charge of R.O. 18. He notices that if he raises the price of his commodity to R.O XXXXXXXXXX), he will...

Hamed own a local gold market that currently has (4693401)subscriber in Instagram at a quarterly charge of R.O. 18. He notices that if he raises the price of his commodity to R.O. (18+ 4), he will lose 8549subscriber. Assuming that subscriptions are linearly related to the price, what price should Hamed charge for a quarterly subscription to maximize his revenue?