Find the missing number???

Find out the number and add your name into Genius List.

If you are an Test Engineer, you should be able to solve it within 3 minutes or less (30 seconds);
If you are a developer, never mind, maybe 1 hour;
If you are an Architect, perhaps you will need 3 hours;
If you are a Doctor, perhaps you will need 6 hours;
If you are an Accountant, maybe 3 months;
If you are a Lawyer, maybe you can never find the answer.
 My designation Test engineer……………urs????

|---+----+----+------+------|
| 2 | 3  | 4  |  15  |  12  |
|---+----+----+------+------|
| 3 | 4  | 5  |  28  |  20  |
|---+----+----+------+------|
| 4 | 5  | 6  |  45  |  30  |
|---+----+----+------+------|
| 5 | 6  | 7  |  66  |  42  |
|---+----+----+------+------|
| 6 | 7  | 8  |  ?   |  56  |
|---+----+----+------+------|
 
Find out the number in "?",