# a block weighing 6.3

Moving at a constant velocity means that the acceleration is zero. So the net force is zero. Therefore the pushing force equals the frictional force. Then the frictional coefficient can be found with $f=2.0=\mu N$ and $N=mg$ is the normal force.
In the second part, the total weight is $W+6.3=N$. Using $f=7.6=\mu N$, one can find $W$.