2) Milan is measuring the density of ethanol. He weighs a bottle three times first empty, then filled with water; then filled with ethanol. Here are his results:
mass of empty bottle = 30.0g mass of bottle filled with water = 90.0g
mass of bottle filled with ethanol = 78.0g
a) Calculate the volume of the bottle.

What are you trying to ask?

Multiply the 3 dimensions, assuming it is a rectangular cuboid, to get the volume in cm³ divide mass by volume to get density in g/cm³

Distance covered = speed x timethe distance traveled going against the stream = distance traveled with the stream.therefore it is the speed and the time that are the variables.as he travels the same distance both ways, speed x time is the same for each way.going upstream his speed is 4 kph; going downstream his speed is 6 kph.therefore we have two simultaneous equations: time upstream x 4 = time downstream x 6time upstream + time downstream = 60 minutestherefore we have the equation: time upstream = 6/10 hour, time downstream therefore = 4/10 hour.distance traveled at 4km/hr in 6/10 hour = 24/10 = 2.4km.check: distance traveled at 6km/hr in 4/10 hour = 24/10 = 2.4km.

Not sure but i think it's b.