12 - 3a for a=3. if a=3, 12 - 3a= ?

3

Step-by-step explanation:

if a=3 then 12-3a = 12-9 = 3

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: