Question

Citia cycles 4.2 km every morning. How many feet are in 4.2 km given that 1 mile=1.609 km and 1 mile=5,280

Answer 1

4.2 km       1 mile            5,280 ft              22,176
             *    ----------    *   -----------    =       -----------  = 13,782.5 feet
                 1.609 km       1 mile                1.609

Using the conversion factors and setting the problem up so that you have km on top and bottom (so that they will cancel), miles on top and bottom (so that they will cancel), your answer will be left in feet.
Multiply across the numerator, then across then denominator. Finally simplify the fraction at the end.