Answer:
gallon
Step-by-step explanation:
Quantity of fruit juice needed by Garrett = 3 gallons
Quantity of grape juice with Garrett =
gallon
Quantity of orange juice with Garrett =
gallon
We need to find quantity of juice he can add to the juice he already has to make exactly 3 gallons of juice.
Quantity of juice he can add to the juice he already has to make exactly 3 gallons of juice = 
Here , LCM ( 3 , 6 ) = 6
So,

On solving terms in numerator , we get 
Therefore ,
Quantity of juice he can add to the juice he already has to make exactly 3 gallons of juice =
gallon .