Hey there!
(78 - x) + (84 - 3x)
= 78 - x + 84 - 3x
= 78 - 1x + 84 - 3x
= (78 + 84) - (1x - 3x)
= (78 + 84) - (x - 3x)
= (1x - 3x) + (78 + 84)
= (x - 3x) + (78 + 84)
= x - 3x + 78 + 84
= -4x + 162
Therefore, your answer should be:
-4x + 162
Good luck on your assignment & enjoy your day!
~Amphitrite1040:)