9514 1404 393
Answer:
9x + 28
Explanation:
The expression is prime if its terms have no common factors. We can look at the factors of the expressions in each column
8x = 2·2·2·x
9x = 3·3·x
6x = 2·3·x
__
42 = 2·3·7 . . . . has a factor in common with every term in column 1
30 = 2·3·5 . . . . same
28 = 2·2·7 . . . . no factor in common with 9x
__
A suitable expression is ...
9x + 28