I wanna know how you find the highest fraction out of 7/8 and 13/15 using the LCM method?

Determine the LCM of 15 and 8 to be 8*15 = 120.
Rename both fractions using 120 as a denominator.
7/8 = (7*15)/(8*15) = 105/120
13/15 = (13*8)/(15*8) = 104/120

You can now determine that 7/8 is the larger fraction.