Calculate the grand average for the following:

$1)5,5,6,7,8$

$2)3,4,5,7,9$

$3)4,6,6,7,9$

$4)5,7,8,9,9$

Group of answer choices

$6\mathrm{.}45$

$5\mathrm{.}00$

$7\mathrm{.}00$

$4\mathrm{.}35$