Let us assume P liters of Diesel added to the mixture so that Diesel will be 25% in the new mixture.According to Question,Quantity of Diesel in 150 liters of the mixture = 20% of 150 = 150 x 20/100 = 30 liters.After adding P liters of Diesel, The total quantity of Diesel becomes (30 + P) and total volume of mixture will be (150 + P).Again According to Question,After adding the P liters of Diesel in the mixture, the Diesel quantity becomes 25% of the new mixture.Quantity of Diesel in new mixture = 25% of Total mixture.? (30 + P) = (150 + P) x 25 %? 30 + P = (150 + P) x 25/100? 30 + P = (150 + P) x 1/4? 120 + 4P = 150 + P ? 4P - P = 150 - 120 ? 3P = 30? P = 10 liters.