Question

A hierarchical memory system that uses cache memory has cache access time of 50 nano seconds, main memory access time of 300 nano seconds, 75% of memory requests are for read, hit ratio of 0.8 for read access and the write-through scheme is used. What will be the average access time of the system both for read and write requests ?
(A) 157.5 n.sec. (B) 110 n.sec.
(C) 75 n.sec. (D) 82.5 n.sec.