All the factors are found when the next value is part of a pair that has already been identified. The difference is 3. The 3rd multiple of seven is 7 × 3 = 21. The 4th multiple of six is 6 × 4 = 24.

Work out the original length of a side that had been enlarged by a scale factor of 7. You already know what the result of the enlargement is (49 cm) and that the scale factor is 7. Remember ...