Answers:
g(s)=4000+0.05s
h(s) = 8000+0.15s
k(s) =2000+0.3s
Explanation:
9) From the expression f(s)=4000+0.15s where s is the monthly sales in dollars we have to convert 5% into a fraction:

∴ g(s) = 4000+0.05x
10) If the base salary of $4000 is double the amount is multiplied by 2:

∴ h(s) = 8000+0.15s
11) If the base salary is cut in half, means $4000 is divided by 2. The commision is multiplied by 2:
∴ k(s) =2000+0.3s