#### Answer

The common difference is $x$.
The next term of the sequence: $4x+4$.

#### Work Step by Step

We are given: $4, x + 4, 2x + 4, 3x + 4, ... $
To find the pattern of this sequence we have to find the difference between consecutive terms of the sequence.
2nd term and 1st term: $x+4 -4 =x$
3rd term and 2nd term: $2x+4-(x+4)=x$
4th term and 3rd term: $3x+4-(2x+4)=x$
The common difference is $x$. We use this pattern to get the next term of the sequence: $3x+4+x=4x+4$