please see attached file:)

I am confused on how to determine the answer, and what fold means.
[attachment id=0 msg=3609]

From the slow step
Rate law = k[H₂] [IBr]
Reaction is first order with respect to H2 and IBr
As concentration is doubled for H₂ and IBr ,rate gets doubled with respect to both of them .
So it will increase 4 folds - due to doubled conc H₂ and doubled IBr