Differentiate between write through and write back procdre in contect of cache memory with suitable example

The access time of a cache memory is 95 ns and that of main memory 1000 ns. It is estimated that 70% of the memory requests are for read and the remaining 30% for write. The hit ratio for read accesses only is 0.8. A write-through procedure is used.

i)        What is the average access time of the system considering only memory read cycles?

ii)       What is the average access time of the system for both memory read and write requests?

iii)      What is the hit ratio taking into consideration the write cycles?