3. Where the relevant event is the discontinuance of payment under regulation C6(5), the employee is entitled to reckon as reckonable service an additional period of
, where—
A is the length of the period during which additional contributions have been paid,
B is the length of the additional period in respect of which the election was made, and
C is the length of the period during which, under regulation C6(3), the additional contributions were to have been paid,
each period being expressed in complete years and any fraction of a year.