JavaScript - let statement

Question

Please help me understand this example
What is this codes output ?
let a = [ 1 , 3 , 5 ] [ 2 ] ;
let b = { x : 4 , y : 10 } .y ;
let c = " 199 " [ 0 ] ;
console.log ( a + b + c ) ;
Answer: 151

Answer 1

a=5
b=10
c="1"
and if you add them you get 151
Now what exactly you don't understand in this?

Answer 2

Why a is 5, b is 10 and c is 1 in quotes? I do not understand