Answer: 18, 43, 68, 93, 118, 143, 168, 193, 218, 243, 268, 293, 318, 343, 368, 393, 418, 443, 468, 493.
Step-by-step explanation:
We are given that the first client is the 18th client and that every 25th afterwards is also selected, so to go about this we can simply take 18 and repeatedly add 25 until we get the 20 clients:
18, 43, 68, 93, 118, 143, 168, 193, 218, 243, 268, 293, 318, 343, 368, 393, 418,
443, 468, 493.