Premise: The XXX BRDC International Trophy was a motor race for Formula One cars held on 19 March 1978 at the Silverstone Circuit, England. It was the 30th running of the International Trophy, and the last to non-Championship Formula One regulations. The race was held over 40 laps of the Silverstone circuit, for a total distance of around 189 km .
Hypothesis: The length of the BRDC International Trophy race is based on how many years it has been held.