The value of a painting was $7000 on may 5, 1970 and $12,000 on may 5,

Hi zatspeed,

I believe that this prompt has a typo in it (which I'll get to in a moment). This question comes down to organization and basic Arithmetic.

We're given the value of a painting on two dates:
1) $7,000 on May 5, 1970
2) $12,000 on May 5, 1975

We're asked for the value of the painting on May 5, 1972.

Fact 1: The value of the painting on May 5,1972, was 20 percent greater than its value on May 5, 1970.

Since the value on May 5, 1972 was 20% greater than $7,000, we can calculate the value....

(1.2)($7,000)

While you don't have to do this math (you KNOW that you can get the value), it's just multiplication. The answer is $8,400.
Fact 1 is SUFFICIENT

Fact 2: The Value of the painting on May 5,1975, was $4,200 greater than its value on May 5,1972

Here, we have to work backwards from the value on 1975. We're told that it's $4,200 greater than on May 5, 1972....we can calculate this value too....

$12,000 - $4,200 = $7,800
Fact 2 is SUFFICIENT

NOTE: When both Facts are individually sufficient, they will both point to the SAME answer. These Facts, while both sufficient, point to different answers. So there's an error in here somewhere.

Final Answer:

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