Consider a cache memory having the hit ratios for read and write operations are 70% and 80% respectively. Cache memory access time is 100ns and main memory access time is 800ns. When miss occurs then 4 word block is copied from the main memory to cache memory. CPU generates 60% write requests and remaining are used for read operations. What is the throughput (or) bandwidth of the cache in terms of million words/sec using Write back policy?