21.
6
Which ratio can form a proportion with 6/9

12/8
8/12
10/12
8/13

Step-by-step explanation:

6/9 divide top and bottom by 3 to get 2/3

Now reduce each of the fractions to the lowest terms, and look for one that gives 2/3.

12/8 = 3/2  (divide by 4 top and bottom)

8/12 = 2/3  (divide by 4 top and bottom)  This is a solution

10/12 = 5/6 (divide by 2 top and bottom)

8/13 (cannot be reduced)

Therefore the second fraction (8/12) forms a proportion with 6/9.

take the logarithm of both sides (the base of the log doesn't matter):

apply the exponent property - this says that :

distribute the log terms on both sides:

group like terms together:

divide through both sides by the coefficient on :

you can do some additional rewriting here using the properties of the logarithm to simplify things if you like: