14.4 Classify each of the following costs as:

●● variable

●● fixed

●● stepped

●● semi-variable.

i) Sales staff members’ mobile telephone charges. There is a basic rental cost irrespective of the number of telephone calls made, plus a charge for each telephone call made, based on the number of minutes the call lasts.

ii) Factory machine oil.

iii) Metered water charges. The bill comprises a charge per unit for the number of units consumed.