135 because 10+5= 15. 15(9)=135. 6-5=1. so 135/1=135
I am going to assume that the equation was supposed to be 
Answer:
It is a polynomial. It is a binomial and it has a degree of 5.
Step-by-step explanation:
A polynomial is an expression consisting of variables and coefficients, that involves only the operations of addition, subtraction, multiplication, and non-negative integer exponentiation of variables so 
will be considered a polynomial.
A binomial is a polynomial with 2 terms.
The degree of a polynomial is the highest exponent in it which in this equation is 5.
On the 1st place he can put 6 textbooks, on the 2nd 5 textbooks etc...
6 · 5 · 4 · 3 = 360
Answer: D) He can arrange textbooks in 360 ways.