This process I am going to walk you through will only work if the quadratic is factorable with nice even numbers, however, you won't have to do all the work before looking to the Quadratic Formula, so pay attention to the cases I put in here, if you follow this step by step you'll be able to factor any quadratic you come in contact with
Step 1: Take out a Greatest Common Factor, in this case we have an integer, but thats okay, it will make multiplication easier later. Our GCF is 3 so we get... 
Step 2: Multiply the R^2 term with the Constant Term ( 2 * 5 ) = 10
Step 3: List the factors of your product from Step 2 ( 10 )
(1 , 10), (2 , 5), (-2 , -5), (-1, -10)
Step 4: When you add those factors together, do any of the sums match your R term? ( 12 )
Since none of the sums add up to give us 12, then we must use the quadratic formula.
In your probelm 
A = 6, B = 24, C = 15 now substitute
Simplfy
Keep Simplifing
Simplfy the radical
Take a 6 out of the denom. & both num. terms
you have two solutions there
Solution 1: 
Solution 2: 
(