Answer:
9s^2 + 17g - 12
Explanation:
(basically combine like terms)
the s^2 are like terms, so that would get you 18s^2 - 9s^2 = 9s^2
then the g’s are like terms,
15g + 2g = 17g
then the -12 is all on its own
if you put it all together:
9s^2 + 17g - 12
