Three numbers are in an increasing geometric progression with common ratio $r$. If the middle number is doubled, then the new numbers are in an arithmetic progression with common difference $d$. If the fourth term of GP is $3 r ^ { 2 }$, then $r ^ { 2 } - d$ is equal to :\\
(1) $7 - \sqrt { 3 }$\\
(2) $7 + 3 \sqrt { 3 }$\\
(3) $7 - 7 \sqrt { 3 }$\\
(4) $7 + \sqrt { 3 }$