The two equal sides of an isosceles triangle with fixed base b are decreasing at the rate of 3 cm per second. How fast is the area decreasing when the two equal sides are equal to the base ?

Question

$(A)\; \sqrt{3b} cm^2/sec$
$(B)\; \sqrt{-3b} cm^2/sec$
$(C)\; \sqrt{3a} cm^2/sec$
$(D)\; \sqrt{5b} cm^2/sec$