The side of an equilateral triangle increases at the rate of 3 cm/sec, then the rate at which the area of the triangle increases when the side is 4 cm, is :

$6\, cm^2/sec$ $6\, \sqrt{3}cm^2/sec$ $\sqrt{3}cm^2/sec$ $6/\sqrt{3}cm^2/sec$

$6\, \sqrt{3}cm^2/sec$