A demand Paging System, with page table held in registers, take 5 ms to service a page fault if an empty page is available, or if the page to be replaced is not dirty. It take 15 ms if the replaced page is dirty. Memory access time is 1ms. Assume we want an effective access time of 2ms and that the page to be replaced is dirty 60% of the time. What is the approximate maximum acceptable page fault rate to meet this access time requirement?