Explanation:
3×5×2 = 30 lorry trips to deliver 2,500 crates.
3 lorries, 5 trips per day, 2 days
that means that one lorry trip transports
2,500 / 30 = 250/3 = 83.33333... crates = 83 1/3 crates.
now we need x lorries each making 6 trips per day in 1 day (so, 6 trips, period) to transport 10,000 crates.
that looks like
x × 6 × 83.33333... = 10,000
x × 6 × 83 1/3 = 10,000
x × (6×83 + 6 × 1/3) = 10,000
x × (498 + 2) = 10,000
500x = 10,000
x = 20
so, we need 20 lorries each doing 6 trips in one day to transport 10,000 crates in one day.
these are altogether 20×6 = 120 lorry trips.
that is 4 times the number of the original scenario (30 trips).
and logically, when doing 4 times the work, we achieve 4 times the result (10,000 crates instead of 2,500).