You want one of the values in the ratio to be one for a unit rate. First, write out the ratio. It is 70 miles/2 hours. It's better not to include decimal numbers when you write a ratio when you can, so we're going to make the hours the unit rate. To make 2 -> 1 hour, divide both sides of the ratio by 2. 70/2 = 35.
The unit rate is 35 mi./hr.
Hope that helped you.
