The least number, which when divided by 12, 15, 20 or 54 leaves a remainder of 4 in each case, is:

524 600 550 544

544

The least number = LCM of (15, 12, 20, 54) + remainder LCM of 15, 12, 20, 54 = 540 Then the number = 540 + 4 = 544 [4 being remainder]