While making the following calculations a calculator is not required, use estimation by powers of two technique.

Question:

we estimate that it would cost about $$1($using average electricity cost in the U$.$S$.)$ to test around $256$ quadrillion $($i$.$e$.,256,000$ trillion$)$ keys.

a$.$ How much would the power cost $($on average$)$ to brute force a $56-$bit DES key?

b$.$ How much would the power cost $($on average$)$ to brute force a $80-$bit Skipjack key?

c$.$ How much would the power cost $($on average$)$ to brute force a $128-$bit AES key?