Condense arrays with reduce ....HELP i can't seem to understand this one

Tell us what’s happening:

Your code so far

var array = [4,5,6,7,8];
var singleVal = 0;

// Only change code below this line.

singleVal = array;

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Link to the challenge:
https://www.freecodecamp.org/challenges/condense-arrays-with-reduce