I'm sure you've gotten this far.
What does "complete the square" mean? We need to add a number to both sides of the equation such that the LHS is a perfect square. My first suggestion is to divide through by 6 to make the coefficient of v^2 one. (This is not necessary, but I find it makes the problem simpler.)
We need to find a number to add to the LHS to make it a perfect square. The only number we can use is the coefficient of the linear term: 3/2. What does that tell us about the number we must add? Check your text and see how far you can get from here.