Question 198509
Al mows lawns at a rate of 30 square feet per minute, 
Bo mows 40 square feet per minute, and Cy mows 60 square feet per minute. 
They accept a job that requires that they mow 6060 square feet of lawn.
 Al begins mowing at 7:00 A.M., but Bo does not begin for another 15 minutes. 
Cy begins mowing at 7:45, and they finish together. 
How long did Bo work?
:
:
Let t = Al's mowing time (minutes)
then
(t-15) = Bo's mowing time
and
(t-45) = Cy's mowing time
:
30t + 40(t-15) + 60(t-45) = 6060
:
30t + 40t - 600 + 60t - 2700 = 6060
:
130t - 3300 = 6060
:
130t = 6060 + 3300
:
130t = 9360
t = {{{9360/130}}}
t = 72 minutes is Al's mowing time
then
72 - 15 = 57 minutes is Bo's mowing time
:
:
Check solution
30(72) + 40(57) + 60(27) = 
2160 + 2280 + 1620 = 6060