What is the value of 'x' if \[\frac{{{a}^{x}}}{{{a}^{y}}}={{a}^{10}}\] and \[{{({{a}^{y}})}^{3}}={{a}^{x}}\] for \[a>1\]?

• A.  \[25\]                                  
• B.  \[5\]                    
• C.  \[20\]                  
• D.         \[15\]