Can someone help me understand these problems please? Should be fairly simple...

Hello All,

I am currently preparing for an upcoming test. I know most of the material but the problems below is what I got stuck on, any help will be greatly appreciated!

A) Determine φ(77) *Euler Totient function for 77+. (The first step is finding the largest number that you can multiply to get 77, i believe which is 7 and 11).

B) -55 Mod 7= 1 (<- I dont understand. I know that -7 mod 55 equals 48 but I can't understand how they got 1 from -55 mod 7).

C)Find the value of x such that: 9 * x 1 mod 10 <- I have no clue