a = pencast
b = pencil cast
c = rubber cast

formula : (48a)+(b/.5)+(c/.25)=20

when a*4=20 ans=5

when b/.5=20 b=10

when c/.25=20 c=5

the answers are:

a=5
b=10
c=5

_Good friends are like stars........You don't always see them, but you know they are always there._