Were you one of the persons that timed the transit of venus so that you could work out the distance between the earth and the sun?
written them down? good, now's the easy bit using those timings to work out the answer, just follow the easy guide here:
another thing is if the orbit of the earth isn't a true circular orbit then the calculations are only "accurate" at one particular point of the orbit and would that be the shortest or longest or inbetween distance?
in the end it all seems a bit hit and miss and i hope they don't use the results when predicting whether an asteroid may hit the earth as i won't feel so reassured next time they say don't worry it will miss us by 40 million miles.