Bob's 9th-grade class is renting out a bowling alley for a party. The bowling alley charges a flat rate of $300, plus an additional $4 per student. So far, 25 students have signed up to attend the party, and more students will probably sign up before the deadline next week.

Find an expression for f(x), the total number of students who will come to the party if x students sign up between now and the deadline.