$7.$ Given that main memory is composed of only three page frames for public use and that a seven$-$page program $($with pages a$,$ b$,$ c$,$ d$,$ e$,$ f$,$ g$)$ that requests pages in the following order:

a$,$ b$,$ c$,$ b$,$ d$,$ a$,$ e$,$ f$,$ b$,$ e$,$ d$,$ f