let abby has a candies, billy has b,charlie has c and david has d

**b=2a**

c=2b => **c=4a**

**d=a+2**

**now all equation are depending only on the value of a .**

it is given that value of **a <4**

now **apply hit and trial for a**=1,2 and 3 .

we get

Abby had 2 pieces,

Billy had 4 pieces,

Charlie had 8 pieces,

and David had 4 pieces.