How to call function outside a scriptblock

I have a function that I should be able to call from any place in my powershell script.

The problem is that it doesn't identify the function in a script block.

In the following example I have the function getNumberFive which should return the number 5.
I want to be able to use this function inside a scriptblock when I start a new job and also in the end of the script.

Expected result:
Write the number 15 to the file "C:\tmp\result.txt"
Write to the console: "I like the number 5"

In reality:
Write the number 10 to the file "C:\tmp\result.txt"
Write to the console: "I like the number 5"

I can workaround this issue by defining the same function inside the scriptblock but then I will duplicate the function and this is not a good programming.

Another way is to define:

$func = {
    function getNumberFive(){
        return 5
    }
}
$scriptBlock = {

    Function printSum(){
        $number = getNumberFive
        $newNumber = 10 + $number  # => $newNumber should be 15
        $newNumber >> "C:\tmp\result.txt"
      }
}
Start-Job -ScriptBlock $scriptBlock -InitializationScript $func

But in this case I won't be able to call $five = getNumberFive.

I read number of methods but I didn't understand how exactly to use them:
CALLING A POWERSHELL FUNCTION IN A START-JOB SCRIPT BLOCK WHEN IT’S DEFINED IN THE SAME SCRIPT

How to pass a named function as a parameter (scriptblock)

https://social.technet.microsoft.com/Forums/ie/en-US/485df2df-1577-4770-9db9-a9c5627dd04a/how-to-pass-a-function-to-a-scriptblock?forum=winserverpowershell

PowerShell: Pass function as a parameter

Using Invoke-Command -ScriptBlock on a function with arguments

My script:

function getNumberFive(){
    return 5
}

$scriptBlock = {

    Function printSum(){
        # $number = getNumberFive => DOESN'T WORK
        # $number = Invoke-Expression ($(get-command getNumberFive) | Select -ExpandProperty Definition) => DOESN'T WORK AS EXPECTED
        # $number = &(${function:getNumberFive}) => DOESN'T WORK AS EXPECTED
        # $number = &(Get-Item function:getNumberFive) => DOESN'T WORK AS EXPECTED
        $newNumber = 10 + $number  # => $newNumber should be 15
        $newNumber >> "C:\tmp\result.txt"
    }

    printSum
}

Start-Job -ScriptBlock $scriptBlock 

$five = getNumberFive
Write-Host "I like the number"$five

Get-Job | Wait-Job
Get-Job | Stop-Job
Get-Job | Remove-Job