Unsure if you're allowed a calculator for this kind of thing but the way i do these is as follows:
Find a common multiple (like most other speed/time/distance problems):
Find what factor of the speeds 60mph is:
AircraftA: 120/60 = 2
AircraftB: 300/60 = 5
This means the Journey can be split into 7 (2+5) parts where AircraftA covers 2 sectors AircraftB covers 5 sectors.
AircraftA covers 2 sevenths of 50miles.
AircraftB covers 5 sevenths of 50miles.
Knowing this use one aircraft to find how far is travelled (smaller numbers are easiest, so use AircraftA)
It covers (50/7)*2 miles at 120mph:
S = D/T
T = D/S = [(50/7)*2]/120 = 0.12 of an hour
Distance: (50/7)*2 miles = 14.28 miles
From AircraftA's takeoff point.
Time: 1000hrs + 7.2minutes = 1007hrs
My apologies if this was too long or anything, but that's how i do maths, blame my professors