A school is planning a field trip for 300 students. They are renting buses and vans. Each bus can hold 40 students, and each van can hold 10 students. The total capacity needed is 300 students. The equation $40B+10V=300$ represents this situation, where $B$ is the number of buses and $V$ is the number of vans. Which of the following is the best interpretation of $40B$ in this context?