Question 1048928
25+35x = 40x reverse the equation 
40x = 25+35x subtract 35x on both sides
5x = 25 
x = 5 hours. At 5 hours the cost is the same. Note that after 5 hours Plumbing Services is cheaper. You can do this easily by plugging in numbers into the equation.
Example: 6 hours
Plumbing = 25+35(6) = 235
Good Guys = 40*6 = 240
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John