Logarithms seem like more trouble than they're worth.
Let (6 is the LCD of 2 and 3).
Thus we get . u^3 comes from the rules of surds, namely:
Solve the polynomial for u and then it should be trivial to find the value of x but remember to check for extraneous results and that any solution is in the domain
edit 2: Hint f(3) = 0
If you don't mean adding them then please clarify what the question wants