How to get element 2 from nested list?

Question

Python

For example a=[1,2,3]
b=[a[1],999],[a[2],100],[a[2],400]
how to get 999 ,100,400 ?
and fold them

Answer 1

You can get it like this:
b[0][1], b[1][1], b[2][1]

Answer 2

sum(x[1] for x in b)