A, B and C made 795 machines at the same time. To make one machine, A needs 6 minutes, B needs 5 minutes and C needs 4.5 minutes. So, how many machines did C make?

1/6 + 1/5 + 1/4.5 = 53/90

So, their output is in the ratios

15:18:20

20/53 * 750 = 283