$4-$ For a three$-$page memory system with memory reference string, for example,

$2,3,6,3,1,1,2,6,2,3,1,6,3,1,2,1,6,3,2,1$

Find the hit ratio for the FIFO replacement scheme

Find the hit ration for the LRU replacement scheme

Find the hit ration for the OPT replacement scheme