University a boasts a 15: 1 student to teacher ratio whereas university b advertises having 150 professors to teach just 3,000 students. if university b wanted to adopt the same student to teacher ratio as univeristy a, would they need to hire professors, or let some go?

So University A has a student to teacher ratio of 15:1.

University B has 3000 students to 150 teachers, which creates a student to teacher ratio of 20:1.

To boast the same student to teacher ratio as University A, University B would need to hire professors to lower their ratio.
 
For example, if they hired 50 more professors so that they had 3000 students and 200 teachers, their ratio would become 15:1 just like University A.

9 + 10 is equal to 19