Question 764435
The problem description and question need to be adjusted to be precise and more sensible.  Here is what they should be:


The first mechanic worked on a car for 20 hours and the second mechanic for 5 hours.  Together they charged $1650.  What was the rate of price per hour of each mechanic if their rates when added together are $135?


Note, the time amounts that each mechanic worked do not come with an indication that they worked at the same time; only that each mechanic worked for a different amount of time.  The question I interpreted is, what does each mechanic separately charge?


Let m = rate per hour for one mechanic
Let n = rate per hour for the other mechanic


We can make two equations.
Account for their rates:  {{{highlight(m+n=135)}}}
Account for total charge:  {{{highlight(20m+5n=1650)}}}


The total charge equation can be divided by 5 to give {{{4m+n=330}}} and then you can choose any reasonable way to solve the system for m and n.