I just got a possible solution from a friend,

7 12 27 47 \_

7 12 27 47 \_ calculate difference

5 15 20 \_ calculate difference

10 5 \_ -> a possible sequence can be taken here, => 0 -5 -10...

so the following 5 15 20 \_ becomes 5 15 20 20

that way we get the 67 in the question as the answer.

this seems logical, but is it a correct way to solve such a problem ?