Your numberFormat function doesn't work and if it did it wouldn't do anything because you haven't assigned it to anything (with an = operator).
Try this:
sum = value[0][1] / val
return "{:.2%}".format(sum)
Or simplify it down to one line:
return "{:.2%}".format(value[0][1] / val)
The funky Python notation tells it to format with 2 digits after the decimal point and show as a percentage. It will then automatically multiply by 100 for you.
Tips:
Post code - not pictures of code (unless you need to show the context of the code). See Wiki - how to post code on this forum.
Leave a little air in your expressions. So, compare,
sum = (value[0][1]/val)*100
sum = (value[0][1] / val) * 100
It's a personal preference but I consider the mathematical operators as separate words and so should have a space each side.