Check if the interval of x is 1 and the interval (difference) between consecutive given numbers of y are the same. If they are the same, the mapping is linear, hence consecutives are obtained by adding the interval (difference) to preceding numbers. Interval/difference = 5 - 3 = 11 - 9 = 2 Since the intervals are the same, the succeeding numbers are obtained by adding the difference to their preceding. p = 5 + 2 = 7 q = 11 + 2 = 13