Answer:
a) this means that his weight was 25% more than baby boys his age and 75% less than baby boys his age. He's in the low percentage of weight and his weight is smaller compared to a large percentile of other baby boys.
b) at 8 months old. Where most baby boys' weight would be more than 8 kg and his is barely over 6 kg. This shows that the estimated increase of atleast 500g weight of a baby is not displayed by his chart and it shows he's undergrowth.