At station A data is send 1500 +100 B/C of MTU 1500
PACKET OF SIZE 1500
At First Router Fragmentation is Done as
456 + 456 + 456 +112
and At second Router Nothing there is No need of Fragmentation So Packet is send as it is to Station B where it Reassemble the Fragmented Part
PACKET OF SIZE 100
there is no need of Fragmentation So, it is send as it is