A plane from Dallas to Boston flies 1,558 miles in 4 hours. About how many miles does this plane fly each hour?
This can be regarded as a 'rate' question because you are comparing two quantities with different units.
You want to know miles PER hour.
In order to calculate the speed in miles per hour, you will divide the distance (in miles) by the time (in hours).
Note the word "about".
We are asked just to estimate, using numbers that are easy to work with, to get an idea of the speed.
1558 miles is close to 1600 miles.
A distance of 1600 miles in 4 hours means about: