How old is the daughter? If she is 10+ she should be able to grasp the very powerful concept of multiplying and dividing units.
Don't think of distance as being d = 129 miles. Think of it as d = 129 * miles. Think of time as being t = 3.45 * hours.
Then think of units that can be multiplied and divided. Suppose you want a final answer of mph. Written out that unit is: miles / hours. See how the units are divided?
Now without knowing any equations at all, you can solve this problem correctly (and ~99% of all math/physics/chemistry problems). Take whatever data you have with the unit of miles and divide that by whatever data you have with the unit of hours:
(129 * miles) / (3.45 * hours) = (129/3.45) * (miles / hours) = 37.4 miles / hour.
See how the units can be moved around using the standard arithmatic rules?
Add one more simple concept and she can solve anything she comes across. What simple concept? You can always multiply by 1 and the answer doesn't change. People have lots of trouble with this concept, so maybe she'll need to be 13+ to understand it. How is it used in this problem? Well, 60 * minutes = 1 * hour. Or rearranging: (60 * minutes) / (1 * hour) = 1. Anytime I want, I can multiply by 1. So anytime I want, I can multiply by (60 * minutes) / (1 * hour) and the answer won't change.
Lets do the problem in minutes. Let t = 207 * minutes and d = 129 * miles. Thus:
d / t = (129 * miles) / (207 * minute) = (129 / 207) * (miles / minute) = 0.623 * miles / minute.
But that isn't the unit I want; I want miles per hour. So lets multiply by 1:
(0.623 * miles / minute) * 1 = (0.623 * miles / minute) * (60 * minute) / (1 * hour) = (0.623 * 60) * (miles*minute/minute/hour) = 37.4 * miles / hour.
Note how the "minute" units cancel, minute / minute = 1. Those two concepts will let your daughter solve just about anything without knowing any formula or ever worrying about units.
