Answer:
x=7
Step-by-step explanation:
9x-9=5x+19
Combine like terms
9x-5x=19+9
4x=19+9
4x=28
x=7
she should add 7 liters of 10% acid solution
Explanation
Step 1
set the equation:
a) let X represents the amount os solution that is 4% acid
let Y represents the amount os solution that is 10% acid
so
I)

if he has 14 liters of 4% acid solution


Step 2
solve the equation :

therefore,
she should add 7 liters of 10% acid solution
I hope this helps you
Its a quadratic trinomial
Its quadratic because the highest degree in the equation is two
Its a trinomial because there are three different terms in the equation