Answer:
a)
, b)
, c) Third day.
Step-by-step explanation:
a) The equation to represent Layla's fees is:

b) The equation to represent Sam's fees is:

c) Both earn the same amount for dog sitting at the third day.
You start off by multiplying the second bracket by -1 to get rid of the bracket.
So,
(2x3 + x2 - 4x) - 9x3 + 3x2 =
2x3 +x2 - 4x - 9x3 + 3x2 =
(2x3 - 9x3) + (x2 + 3x2) - 4x =
-7x3 + 4x2 - 4x