Basic JavaScript - Understanding Uninitialized Variables

Hi devs!, what is my error, I have been looking for it but not.
Thanksss!

Your code so far

// Only change code below this line
var a;
var b;
var c;
// Only change code above this line

a = a + 1;
b = b + 1;
c = "I am a";

var a = 6;
var b = 15;
var c = c + "String!";


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Challenge: Basic JavaScript - Understanding Uninitialized Variables

Link to the challenge:

Ignoring this comment is a problem. It breaks the tests

You shouldn’t re declare the variables. You must set the initial value of the first declaration