Answer:

Step-by-step explanation:
Given,
Total quantity of solution = 11 gallons
Initial detergent in the solution = 18 % of 11 gallons



Now, here g represents the number of gallons of water she should add to make 12 % detergent solution,
Final quantity of solution = ( 11 + g ) gallons
Thus, we can write,
The part of detergent in (11+g) gallons of water = The final percentage of detergent

Which is the required equation.