(a)

All 3 drivers meet again at the lowest common denominator of the 3 trip intervals.
LCD(30,18,25) = 450

To get the above result, first do prime factorisation of all the trip intervals:
30 = 2 x 3 x 5
18 = 2 x 3^2
25 = 5^2

The lowest common denominator will be the product of the highest power of each prime factor that appears:
2 x 3^2 x 5^2 = 450

Now, 450 mins = 7 hours 30 mins
Hence, all 3 drivers meet again at 0600 hrs + 0730 hrs = 1330 hrs (1:30pm)

(b)

Earnings = $9 x 2 x 12 x 6 x 4 = $5184
Costs = $2000 + $150 + ($70 x 6 x 4) = $3830

Yes, Mr Lim will be able to cover his costs from his earnings