You can put this solution on YOUR website! I traveled from A to B at 100km/h. The trip would take me 3 hours more at 80km/h. How far is it from A to B?
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d = distance from A to B
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d = 100 km/hr * t ---- t in hours
d = 80*(t+3)
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d = 100t = 80t + 240
20t = 240
t = 12 hours
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100*t = 1200 km