Answer:
I answered this on your other one but what ever.
arrow= positive 15
bone= positive 721
clay bowl= 0 (zero is neutral which means it's neither positive or negative)
necklace= positive 462
basket= negative 1,200 (-1,200)
For the second part
It's like a graph. sea level is the 0. The word 'above' would mean a positive number. The word 'below' would be a negative number because it is less than 0 or in this case sea level.