.
If you just know proportions, you may solve the problem, as Ewind does in his post.
But you can solve it even if you don't know what a proportion is.
For it, you calculate the rate first, using given distance and time
    rate =  = 67 miles per hour
and then find the distance under the problem's question
    distance = 5*67 = 335  miles.    ANSWER
 = 67 miles per hour
and then find the distance under the problem's question
    distance = 5*67 = 335  miles.    ANSWER