How to use the Periodically Compound Interest formula (see details)?

hi im stuck at the questiona bout this. the Continuosly compounded formula is easy but i cant see to find the periodically compound one ( the one missing is the time in years or t)

the question goes like this:

How long does it take money to double in value for the specific interest rate?

Question is: What is the doubling time of an investment earning 12% interest if the interest is compounded every 2 months

i use the formula

A=P*(1+r/n)^nt

A= 2

P=1

i assigned those 2 constants because the question itself doesnt have one and the question says: "doubling time" so its just times 2, for simplicity i used 1 as the principal. correct me if im wrong ^^ or if i used the wrong formula

Best answer goes to someone who answers it in 1 hr