Question A
Hourly rate 
A plus plumbing=60hr
Quality plumbing 50hr
One time fee 
A plus plumbing $80
Quality plumbing $150
Question B
A plus plumbing cost $60 and hour and has a one time fee is $80
Explanation 
At zero hours it’s $80
For the rate it’s 
140-80=60 
320-80=240 240/4=60
Question C
Quality plumbing charges $50 and hour and has a one time fee of $150
Explanation 
At zero hours it’s $150
For the rate it’s 
200-150=50
250-150=100. 100/2=50
Question D
Yes they can 
Find two equations for the rates and fees 
So,
60h+80=50h+150 and solve for h 
60h-50h=10h and 150-80=70 
10h=70 the. Divide h=7
So for seven hours they will be equal