I got a much lower profit. Did everyone else minus the cost of the balls from the selling price? Giving 50p for slow and 25p for medium/fast?
And for the last question: lowest was 1, highest was 5. (It couldn't be 6 as there's only 5 other verticies and it can't loop back to itself as it's a 'simple'graph). Got x=4 as well though.