Question 500880
Let x  be the location of Porshe car and y  be the lcoation of VW
distance between x and y = 450 miles
speed of porshe = a
speed of VW = b

b = 2a  -> equation 1(speed of 1 car is twice the other) 

After 5 hours, the cars meet. 
i.e., both the cars together would have covered the 450 miles in between them
distance = spped * time
and hence 5a + 5b = 450
dividing by 5,
      => a+b = 90
         3a = 90  (from equation 1)
a = 30
b = 2a = 60

Hence the speed of the cars are 30 miles/hour and 60 miles/hour

Check: 5a + 5b = 450 => 5*30 + 5* 60 = 150 + 300 = 450