ECO - Preferences and Utility

Preferences and Utility 
1. Consider the Cobb Douglass utility function U(X, Y) = X^(1/6)Y^(5/6) of a typical student. X denotes time spent studying and Y denotes time spent socializing. Use calculus in your answer. 
A. Is the “more is better” assumption satisfied for both goods? 
B. Is there diminishing marginal utility for both goods? 
C. Is there a diminishing marginal rate of substitution?