Hey there!
4a + (-1.2b) + (-3a) + 7.9b
REWRITE/REWORD:
= 4a - 1.2b - 3a + 7.9b
COMBINE the LIKE TERMS:
= (4a - 3a) - (1.2b + 7.9b)
= 4a - 3a - 1.2b + 7.9b
= 1a - 6.7b
= a - 6.7b
Therefore, your answer is: a + 6.7b
Good luck on your assignment & enjoy your day!
~Amphitrite1040:)