Computing average access time


A computer has a cache memory and a main memory with the following features: 

– Memory cache access time: 4 ns – Main memory access time: 80 ns – The time needed to load a line in cache is 120 ns. – Write-through policy. If the hit ratio in this computer is 95 % and the 90% of the memory accesses are read operations, what is the average access time?

It seems a bit weird to me since I have read through this site calculate the effective (average) access time (E AT) of this system but I still do not know how to do it. I would appreciate any help. Thanks!