Hi guerrero,

This type of question requires a mix of "brute force", Number Properties and TESTING THE ANSWERS.

Here, we're told to form three 2-digit numbers (with the digits 1,3,6,7,7,7) that add up to a PRIME. We want the LARGEST POSSIBLE PRIME.

Let's take a look at the answers. We'll start with the largest:

219

We can quickly eliminate this answer because it's NOT PRIME (it's divisible by 3).

So, try the next largest number:

211

It IS prime. We know that to get to 211, we'll need some "bigger" 2-digit numbers. Playing around with the digits a bit, we can get:

67 + 71 + 73 = 211

This answer fits everything that we're told.

Final Answer: D

GMAT assassins aren't born, they're made,
Rich