The least common denominator (LCD) is 1.
56 is the lcd of 8 and 7. You can get this by multiplying 8x7. 8 and 7 have no common factors; that is why you multiply the two numbers to get the lcd.
The LCD of x, 5, 7, 15 is 105x.
LCD(7, 8, 2) = 56.
105
LCD(8, 15) = 120
LCD is 24
56
It is done by: 7*8 = 56
7 is prime, and 15 is not a multiple of it, so the answer is 1. ■
LCM(15, 5, 8) = 120
105