According to market research, the number of magzine subscriptions that can be sold can be estimated using this function
`n(p)=(5,000)/(4p-k)`, where n is the number of thousands of subscriptions sold, p is the price in dollars for each individual subscription, and k is some constant. If 250,000 subscriptions were sold at $15 for each subscription, how many subscriptions could be sold if the price were set at $20 for each subscription?