A radioactive isotope X with a half-life of \[1.37\times {{10}^{9}}\] years decays to Y which is stable. A sample of rock from the moon was found to contain both the elements X and Y which were in the ratio of 1 : 7. The age of the rock is

• A.            \[1.96\times {{10}^{8}}\]years                                         
• B.            \[3.85\times {{10}^{9}}\]years
• C.            \[4.11\times {{10}^{9}}\]years                                         
• D.            \[9.59\times {{10}^{9}}\]years