Question 392239
18/3 = 6 km/hr
18/1.5 = 12 km/hr
The boat's speed is the average = (6 + 12)/2 = 9 km/hr
The current speed is the difference = 3 km/hr
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I already tried:
d = 3(r-18) d = 1.5(r+18)
d = 3r - 54 d = 1.5r + 27
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If you include units, you'll see that your approach is not right.
d = 3(r-18) d = 1.5(r+18)
r-18 --> km/hr - km  The units don't match, so something's wrong.  Using the units can help to avoid mistakes.