How do i calculate 5^7(mod 77)

I know fermats theorem is used somewhere but i dont know how to use it- so step by step please!!
Thanks.

If the question was , How do I calculate 5^7(mod7) ?, then Fermat's (Little) Theorem could be used.

Theorem : If p is prime and (a,p) = 1 then a^(p - 1) Ξ 1 (mod p)
Then 5^6 Ξ 1 (mod7)
So, 5^7 = 5 x 5^6 Ξ 5 x 1 (mod7) Ξ 5 (mod7)

5^7(mod77) is just hard work.
5^3 = 125 Ξ 48 (mod77)
5^4 = 625 Ξ 9 (mod77)
5^7 Ξ 9 x 48 (mod77) Ξ 432 (mod77) Ξ 47(mod77)