Answer: 591
Explanation:
From the digit 1, 9 and 5. The following numbers can be gotten if we use the 3 numbers.
159
195
519
591
915
951
Of all the numbers, the closest to 600 are 519 and 591.
To the nearest 100, 519 gives 500 while 591 gives 600. Therefore, the answer is 591.