Answer:
15.) -21f - 16
16.) 5s + 2t
Explanation:
15.)
-12f - 16 - 9f (Distribute 4 through the parentheses)
-21f - 16 (Collect like-terms)
16.)
4s + 2t + s + s - s (Since two opposites add up to zero, remove them from the expression)
4s + 2t + s (Collect like terms)