Read the question. What is the number of page faults for LRU, FIFO and Optimal

Assume that a physical main memory contains $3$ page$-$frames. Given the following page reference sequence:

$7,2,3,1,2,5,3,4,6,7,7,1,0,5,4,6,2,3,0,1.$

Oa$.$ Page faults using LRU $=17,$ using FIFO $=16,$ using optimal replacement $=13$

Ob$.$ Page faults using LRU $=17,$ using FIFO $=16,$ using optimal replacement $=12$

Oc$.$ Page faults using LRU $=18,$ using FIFO $=17,$ using optimal replacement $=12$

Od$.$ Page faults using LRU $=18,$ using FIFO $=17,$ using optimal replacement $=13$