Afurnace used of the fuel in its tank in the month of march then used of the remaining fuel in the month of april. the beginning of march. there were 240 gallons of fuel in the tank. how much fuel in gallons was left the end of april

X= tank volume
March used 40% of x=(40/100)x=2x/5
Remaining=x-(2x/5)=3x/5
April used 25% of 3x/5=(25/100)(3x/5)=75x/500=3x/20

therefore:

3x/20=240
x=(240*20)/3=1600

Then, the tank volume is 1600 gallons, 
x=1600

Fuel in gallons was left the end of April= Remaining (at March)-April used.

Fuel in gallons was left the end of April=(3x/5) - (3x/20)=9x/20
Therefore:

9x/20=9*(1600 gallons)/20=720 gallons.

the end of April  was left 720 gallons.