I am going to assume your question has an error, and 16 people play tuba in the band. Otherwise, there is not enough information to answer the question.
If you want to know the total number of students, you would multiply 16 students by 5. (We know 16 students is 20% of the band. You need to know the number of students that make up 100% of the band, and 20 goes into 100 5 times.)
In conclusion, there are 80 students total in the band.
