Hey there!
9 - 3x + x - 15
= 9 - 3x + 1x - 15
COMBINE the LIKE TERMS
= (9 - 15) + (-3x + 1x)
= (-3x + 1x) + (9 - 15)
= (-3x + x) + (9 - 15)
= -3x - x + 9 - 15
= -2x - 6
Therefore, your answer should be:
-2x - 6
Good luck on your assignment & enjoy your day!
~Amphitrite1040:)