Since the train travels at a rate of 70 miles/hour, the train will take 5 hours to have traveled a total of 350 miles. The missing information in the question you've proposed is the value of "H" or the number of hours (as the unit hours is indicated in the question). This can be determined with the formula Distance = rate X time. 350 = 70 X H, in this case. To isolate the variable H, 70 (the rate) divides 350 (the total distance) into 5. 350 ÷ 70 = H. 5 = H, the amount of time spent traveling for 350 miles at a rate of 70 miles/hour.