Answer:
(a) The net profit for walking 3 dogs is $40
(b) The net profit for walking 6 dogs is $100
Explanation:
There are mistakes in your question; however, the correct given parameter is

Required
Interpret p(3) = 40 & p(6) = 100
Interpreting p(3) = 40
Comparing this to

d = 3 & p(d) = 40
This implies that:
The net profit for walking 3 dogs is $40
Interpreting p(6) = 100
Comparing this to

d = 6 & p(d) = 100
This implies that:
The net profit for walking 6 dogs is $100