Let's assume
length of Ribbon A is A
length of Ribbon B is B
length of Ribbon C is C
we are given
A=B+20% of B
A=1.2B
B=C-20% of C
B=0.80C
now, we can find relation between A and C
A=1.2B
we can plug B
A=1.2*0.80C
A=0.96C
so,
Ribbon A is 4 % shorter than Ribbon C.......Answer