A number which precedes a variable is called a coefficient. Now, if that coefficient can be expressed in the form a/b with a and b integers, then a/b is a rational number (those are the fractions and the integers), thus that number is a rational coefficient.
180 < 75 + 0.10m 180 - 75 < 0.10m 105 < 0.10m 105 / 0.10 < m 1050 < m.....this is minutes, we need hrs 1050/60 < m 17.5 < m.......the guest would have to spend more then 17.5 hrs