five less than the quotient of a number and 4 is 15. What is the number?

A quotient is generally the result of division such as: 10/2=5 is the quotient.

If you mean "any number", then we have:

q-5+4=15

q=16

Call the number N

 

N/4  -  5 = 15   so  N/4  =  20   so  N = 4*20  or  N = 80