Question 884315
Let c be the speed of the car and a be the speed of the airplane.
Hence a = c+310  -> eq 1
Let t be the time taken for car and plane to cover a distance of 120 miles and 1050 miles respectively.

distance = speed * time

For car:
ct = 120 -> eq 2

For plane:
at = 1050 -> eq 3

substitute for a from eq 1 in eq 3
(c+310) = 1050 -> eq 4

Eq4/eq 2
becomes
(c+310)/c = 1050/120
(c+310)/c = 35/4
=> 4c + 1240 = 35c
=> 31c = 1240
=> c = 40 miles per hour
Speed of car  = 40 miles per hour
Speed of plance = 350 miles per hour