Answer:
"TypeError 'int' or 'float' object is not callable" It probably means that you are trying to call a method when a property with the same name is available. If this is indeed the problem, the solution is easy. Simply change the method call into a property access.
In your case you may change the things
return <variable>
with
return str(<variable>)
So you should program like
from __future__ import division
x = 66
y = 99
z = 33
str(round((x/y)*0.8*z))
Hope you understand. Happy coding.