Answer:
15 hours of work would both plumbers charge the same amount of money for the job.
Step-by-step explanation:
Let us assume the number of hours Richard works = m
Per hour charge = $45
So, the charge for working m hours = m x $45 = 45 m ....... (1)
Let us assume the number of hours Spiro works = m
Per hour charge = $35
So, the charge for working m hours = m x $35 = 35 m
Also, the charge for parts = $150
So, total amount Spiro charges = Cost for m hours + Charge for parts
= 35 m + $150 ...... (2)
Now, for m hours as they charge the SAME AMOUNT.
⇒ From (1) and (2), we get
45 m = 35 m + $150
or, 45 m - 35 m = 150
or, 10 m = 150
⇒ m = 150/10 = 15
or, m = 15
Hence, 15 hours of work would both plumbers charge the same amount of money for the job.