A fisherman catches fish at a poisson rate of two per hour from a large lake with lots of fish. Yesterday, he went fishing at 10:00am and caught just one fish by 10:30am and a total of three by noon. What is the probability that he can duplicate this feat tomorrow?

I think lambda is equal to 4 so the formula f(x)=3^x*e^-3/(3!) but that I dont know what to do from here? Any help would be grateful