We can solve this problem using a proportion:
28 copies per minute = x copies per t minutes
where x is the number of copies we want to make (126) and t is the time it takes to make that many copies. Solving for t, we get:
28 copies per minute = 126 copies per t minutes
28t = 126
t = 126/28
t ≈ 4.5 minutes
Therefore, it takes about 4.5 minutes to make 126 copies on this copy machine.