Df = g - 10
To solve for d, divide both sides by f.
df / f = (g - 10) / f
d = (g - 10) / f
I hope this explains it.
To find the lowest common denominator you need to know the factors of 5 and 11.
So make two lists:
5, 10, 15, 20, 25, 30, and so on.
11, 22, 33, 44, 55, 66, and so on.
Keep doing that until you find the lowest common number in the lists. The LCD will be 55.
Log7 36 is the correct answer.