Since there are two unknown you need two equations. X = the fast car. Y = the slower car.
y = x + 5
since the faster car is 5 mph faster
3x + 3y = 423
since they travel 3 hours.
then we have to substitute the value of y into the second equation.
3x + 3(x + 5) = 423
divide both sides with 3
2x + 5 = 141
2x = 136
x = 68
Now that we now x we can use the first equation to get y.
y = 68 + 5
y = 73
Answer: The slow car travels at 68 MPH and the faster car travels at 73 MPH.
