Calculate the binocular prismatic effects of the following:

a. Right eye 4 prism dioptres, base-out 
    Left eye 3 prism dioptres, base-out

b. Right eye 5 prism dioptres, base-out 
    Left eye 6 prism dioptres, base-in

c. Right eye 3 prism dioptres, base-up 
    Left eye 4 prism dioptres, base-down

d. Right eye 2 prism dioptres, base-up 
    Left eye 3 prism dioptres, base-up