Water flowing from a faucet can fill 1/4 of a tank in 3 minutes. how long does it take to fill the tank completely with water? how long will it take to fill 6 similar tanks completely with water

1/4 of a tank in 3 minutes.

four 1/4 is equal to a whole (here it's tank)
so if the value of 1/4 is 3 and other 1/4 + 1/4 + 1/4 is 3 + 3 + 3

So to fill one full tank it takes 12 minutes.
(Value of whole is 12)

So now you have six different tanks, assuming they are filling at different time.

now 6 whole and each whole has value of 12.
In other words one tank in 12 min, so how long for 6 tanks.

6 * 12 = 72 minutes.
or
12 + 12 + 12 + 12 + 12 + 12 = 72 minutes.
(Each 12 minutes represents a tank)

72 minutes

//Hope it helps