Remember, any band showing in the child's profile must be present in the mother OR father's profile, OR both. If not, that man is not the child's father.
Step 1: Look at the child's first DNA band (labelled 1)
The mother possesses this same band, so the child could have inherited that DNA from its mother. It is therefore needless to look at whether any of the men possess that band
Step 2: Look at the child's second DNA band (labelled 2)
The mother does not possess this band, so the child must have inherited it from its father. Only men B and D possess this band, so men A and C are eliminated
Step 3: Look at the child's third DNA band (labelled 3)
As with band 1, the mother possesses this same band, so the child could have inherited that DNA from its mother. It is therefore needless to look at whether any of the men possess that band
Step 4: Look at the child's fourth DNA band (labelled 4)
The mother does not possess this band, so the child must have inherited it from its father. Only men A, B and C possess this band, but A and C have already been eliminated
Step 5: Conclude that B is the father
Step 6: Look for supporting evidence from band 6
The mother does not possess this band, and the only man who possesses it is B. This reinforces the conclusion that Man B is the child's father