SPEED        TIME                    DISTANCE

Jet          r+375        1350/(r+375)             1350

Car           r            300/r                    300

Difference                   1

Let x be the speed of the car, in miles per hour.

Then the speed by the jet is  (x+375) mph, according to the condition.


The time spent by the car is   hours.


The time spent by the jet is   hours.


The difference is 1 hour, which gives you an equation


     -  = 1.


It is the "time" equation.

To slve it, multiply both sides by x*(x+375). You will get


    300*(x+375) - 1350x = x*(x+375),


Simplify and solve for x


     300x + 300*375 - 1350x = x^2 + 375x

     x^2 + 1425x - 1112500 = 0

      =  = .


Of the two roots, only positive root  x =  = 75 makes sense.


So, the car's rate is 75 mph;  the jet rate is  (75 + 375) = 450 mph.    ANSWER


CHECK.   -  = 4 - 3 = 1,  exactly in accordance with the condition.