Ex. 1.17_ Finding the physical address from a virtual address in a contiguous memory allocation scheme. Given a virtual address, how would you f ind the corresponding physical address if you know the first physical address of the program to be loaded? Give a mathematical formula. Ex. 1.20_What is the round-robin scheduler? Ex. 1.22-A timer is a hardware device. It can generate an interrupt signal at a predefined time interval. Explain how a timer device is used for the round-robin scheduling in multi-tasking operating systems