Each person should ride the bike for 4 miles, so that every one has to walk 8 miles and ride 4 miles.
If they had 2 bikes, each person will ride for 8 miles, 4 miles on each bike, and then walk 4 miles.
If we assume the club membership includes
then the blanks in the Juniors circle must be filled in with 6 and 8 (with the 8 going in the overlap with girls). The remaining blank in the Girls circle must be filled in with 12, the number of senior girls. The blank outside both circles is the number of senior boys (members who are not juniors and not girls), 16.
The speed of a bus that travels 250 km in 2 hours is 145 because you have to divide 250 km and 2 hours which gives 145.
Hope this helps:)