A body of mass m ascends from the earth's surface with zero initial velocity due to action of two forces as shown. The force $F$ varying with $h$ as $\hat F=-2m \vec {g} (1-ah)$ where a is constant. Find the maximum height atained by the body t
$(a)\;\frac{1}{ga} \quad (b)\;\frac{1}{a} \quad (c)\;\frac{1}{2a} \quad (d)\;\frac{g}{2a}$