General Properties:

If a function f(n) is O(g(n)), then there exists a scalar constant a such that a * f(n) is also equals to O(g(n))
e.g., Suppose, f(n) = 2 * n + 5 which is O(n), then7 * f(n) = 14 * n + 35 = O(n) 
Reflexive: If f(n) is given, then f(n) is O(f(n))
e.g., Suppose, f(n) = n + 3, then f(n) = O(n) 
Transitive: If f(n) = O(g(n)) and g(n) = O(h(n)), then f(n) = O(h(n))
e.g., Let f(n) = n, g(n) = n^2, and h(n) = n^3,
From reflexive Property: f(n) = O(n), g(n) = O(n^2), and h(n) = O(n^3)
then, f(n) = O(n^3) is True.
Please refer Asymptotic Notations  Big Oh  Software Development  Discussion Forum  Board Infinity to find why the above equation is True.