By adding up the calculations in a science questions. For example if an apple is 86.3 density, and an orange is 23.2 density, and if the question asks you how much more is the apples density than the...
Either define finite first (usually as equivalent to a set of the form {1,2,3,...,n} for an integer n, in which case infinite is not finite; or use a set is infinite if and only if it is equivalent...