Abarrel contains 1513 liters of water. 34 of the water was used to water plants.
how many liters of water was used to water plants?
how many liters of water are left in the barrel?

Considering that 34% of the total quantity of water was used to water the plants we can get to the solution of the problem.
Total quantity of water in the barrel = 1513 liters
Percent of water used for watering the plants = 34%
Then
Quantity of water used to water the plants = (34/100) * 1513
                                                                     = 514.42 liters
So 514.42 liters of water was used from the barrel to water the plants.
Quantity of water left in the barrel = 1513 - 514.42 liters
                                                      = 998.58 liters
So the quantity of water that is left in the barrel after watering the plants is 998.58 liters.
If you have said in the question that 3/4 of the total quantity of water was used for watering the plants, then the solutions would be as given below
Quantity of water used for watering the plants = (3/4) * 1513 liters
                                                                          = 1134.75 liters
Amount of water left in the barrel after watering the plants = 1513 - 1134.75 liters
                                                                                             = 378.25 liters.