Answer
$a=56.88\frac{m}{s^2}$
Work Step by Step
First we calculate the weight force:
$W=mg=(3kg)*(9.79\frac{m}{s^2})=29.37N$
Then the net force acting on the rock upside direction is:
$F_{net}=F_{up}-F_{weight}=200N-29.37N=170.63N$
Now we have the net force we can calculate the acceleration according to the Newton's second law:
$a=\frac{F}{m}=\frac{170.63N}{3kg}=56.88\frac{m}{s^2}$
