i don’t really understand what they are asking…

Firstly, welcome to the forums.

While we are primarily here to help people with their **Free Code Camp** progress, we are open to people on other paths, too. *Some* of what you are asking is pretty trivial in the Free Code Camp context, so you might find that if you’re not getting the instruction and material you need in your current studies, the FCC curriculum will really help you get started. At a modest guess I’d say investing a 4-5 hours working through the curriculum here will really pay off. You can find the curriculum at https://www.freecodecamp.org/learn.

With your current questions, we don’t have enough context to know **what you already know or don’t know**, so it is impossible to guide you without just telling you the answer (**which we won’t do**).

It is pretty typical on here for people to share a codepen / repl.it / jsfiddle example of what they have tried so that anyone helping has more of an idea of what help is actually helpful.

Please provide some example of what you’ve tried and I’m sure you’ll get more help.

Happy coding

```
// you have to create a function that takes a input
function validate(string) {
//you have to strip off the last digit (in this case 9)
let lastDigit = Number(string.split('').pop())
// create an array of the given string
let numberArr = string.split('')
//declare a new array to keep some numbers afters taking data from numberArr
let newNumberArr = []
// now take the data from the numberArr and multiply 1 for the even indexed value and 3 for the odd indexed value except the last value in NumberArr
for(let i = 0; i < numberArr.length - 1; i++) {
if(i % 2 === 0) {
newNumberArr.push(Number(numberArr[i] * 1))
}
else {
newNumberArr.push(Number(numberArr[i] * 3))
}
}
//now calculate the total of all numbers in newNumberArr
let total = newNumberArr.reduce((acc, curr) => acc += curr)
//store the remainder of it by dividing the total by 10
let remainder = total % 10
// and lastly check that 10 - remainder is equal to the last digit (such as 9)
if((10 - remainder) === lastDigit) return true
return false
}
console.log(validate('2210528857729')); //should return true
```

thank you, really helpful with your comments. I will break it down line by line and learn from this thanks again!

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