x is the number of gallons of milk that has 6% butterfat.
y is the number of gallons of milk that has 1% butterfat.
As the farmer will create 225 gallons of milk: x and y needs to sum 225
To describes the butterfat that has the milk, write the percentage as decimals and multiply corresponding number of gallons for the decimal butterfat that it has.
6% is 0.06
1% is 0.01
5% is 0.05
Then, the system of equation that describes the situation is: