我的增强加法Javascript不起作用

Question

var a = 3;
var b = 17;
var c = 12;

var a = a + 12;
var b = 9 + b + 2;
var c = c + 7:

/* Should Equal to 
a = 15
b = 26
c = 19
/*

即使我尝试过有人可以帮助我解决我的问题，我的代码也无法运行？

Answer 1

var a = 3;
var b = 17;
var c = 12;

a = a + 12;
b = 9 + b + 2;
c = c + 7;

Answer 2

var a = 3;
var b = 17;
var c = 12;


a += 12;
b += 9;
c += 7;

尝试...