Apparantly this Math problem is impossible? Ive posted it like 10 times and yet nobody has answered.​

Samantha swam upstream for some distance in one hour. she then swam downstream the same river for the same distance in only 12 minutes. if the river flows at 4 mph, how fast can samantha swim in still water?

Simplify the expression. -2/5(10+15m-20n)

Awater tank holds 18000 gallons. how long will it take for the water level to reach 6000 gallons if the water is used at anaverage rate of 450 gallons per day