The tension on the rope pulling the bucket upward is equal to the sum of all the downward forces. These forces are the weight of the bucket and the force that accelerated it.
T = mg + ma
T = (6 kg) x (9.8 m/s²) + (6 kg) x (3 m/s²)
T = 76.8 N
Thus, the tension is 76.8 N.