r:b=5:6 and we are adding an equal amount of white as there is red and blue so:
r:b:w=5:6:11
This means that there is a multiple of 5+6+11=22 parts of the whole...
55L/22p=2.5L/p that means that each part is equal to 2.5L.
Since there are 5 red parts, Jake will need 5(2.5)=12.5L
So Jake will need 12.5 liters of red paint.