Mario is making fruit punch by mixing orange juice and pineapple juice should he use to make 3 litres of fruit punch?

The complete question in the attached figure

we know that
the ratio is 1:3
that means 
(1+3)=4 liters
To prepare 4 liters of fruit punch use 1 liter of orange juice and 3 liters of pineapple
so
to Make 3 Liters of fruit punch
the proportion to find the pineapple liters will be
3/4=x/3------> x=9/4-----> 2.25 liters of pineapple

the answer is
2.25 lt pineapple