According to market research, the number of magazine subscriptions
that can be sold can be estimated using the function
$$n(p)=\frac{5,000}{4p-k}$$
where n is the number of thousands of subscriptions sold, p is the price
in euros 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?