Question 697598
My car speed = x mph
Adam's car speed - y mph

Time = distance / speed

Time adams for 250 miles = 250/y

My time = (250/y) - (4/5)................... 48 minutes = (4/5) hours

192/x = (250/y) -(4/5).........................(1)

(250/y) = (192/x) +(4/5)

Second condition 

My time = Adam's time. But different distances

(300/x) = (250/y) 
(300/x) = (192/x) +(4/5)  substitute (250/y) in equation (1)


(300/x)-(192/x) =4/5

108/x= 4/5

4x= 540
/4
x= 135 mph  ( My speed)

Plug x 

(300/x) = (250/y)
(300/135) = (250/y)

y= (250*135)/300
y= 112.5 mph  ( Adam's speed)