Assistance needed to apply a formula

Morning all ... really quick question, as I think i'm being a dunce!

How do i get;

{=SUM(LEN(Tracker!I7:I401)-LEN(SUBSTITUTE(Tracker!I7:I401,"In Progress","")))/LEN("In Progress")}

I seem to remember something along the lines that I need to "CTRL + <insert key>" to apply this due to the type of formula that it is to get it to apply and work ...

any help is appreciated.

Thanks in advance!

it is ctrl+shift+enter to confirm an array formula