Question 1074383
(140/x)+(63/(x-7)) = 3  
The common denominator is x(x-7). Join both equations into one:
7(29x-140)/(x(x-7)) = 3
7(29x-140) = 3x(x-7)
203x-980 = 3x(x-7)
203x-980 = 3x^2-21x
-3x^2-21x+203x-980 = 0
-(x-70)(3x-14) = 0
(x-70)(3x-14) = 0
x-70 = 0 or 3x-14 = 0
x = 70 or x = 14/3
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Let's try the 70 first:
140/70 = 2
63/(70-7) = 1
2+1 = 3 hours This is the correct answer.
:
John