LCD(15, 7, 8) = 840.
The LCD of x, 5, 7, 15 is 105x.
The LCD is 56. The two have no common factors, so the LCD is their product, 7 x 8 =56
LCD is 24
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.
It is done by: 7*8 = 56
120
360
7 is prime, and 15 is not a multiple of it, so the answer is 1. ■
168
280
280
56565656