Covering radius of a code in the Hamming space
It's easier to remove from your table all lines with codes already in C. In your case only two lines will remain, minimum distance in both lines are 1, so the maximum distance of these two is max(1,1)=1

Overall, the algorithm is the following:


for each possible code x, find the closest element c in C (i.e. the one with minimum distance d(x,c)) and record this distance
find the maximum of all distances recorded at the previous step


I find that it's well visualized with set of spheres covering part of 3D space. You check all points outside of spheres and find one that has the largest distance to its closest sphere.