Please Math help please?

Let x be the amount of 10% solution needed

Let y be the amount of 20% salt solution

x+15=y

.1x+.4(15)=.2y

.1x+6=.2y -multiply by 10 to remove the decimals

1x+60= 2y

x+15=y

Solve the system

x=y-15

1(y-15)+60=2y

y-15+60=2y

45= y

x+15=45

x= 30

Therefore, you would need 30 liters of a 10% solution to get 45 liters of a 20% solution

x liters of 10% solution will yield .10x salt

15 liters of 40% salt solution will yield .40(15) = 6 liters salt

(x + 15) liters of 20% solution will yield .20(x + 15) liters salt

balance the salt...

.10x + .40(15) = .20(x + 15)

.10x + 6 = .20x + 3

3 = .10x

x = 3 / .10 = 30

so 30 liters of 10% solution (3 liters of salt) mixed with

15 liters of 40% solution (6 liters of salt) will produce

45 liters of 20% solution (9 liters of salt)