From the given information, what is the equivalent uniform annual cost (EUAC) of computer B?

The solution is as follows:

Can someone explain what's going on in the middle of the solution? Most specifically:

...+ $275 + ($425 - $275) (P/A, 6%, 5) x (P/F, 6%%, 8)(A/P, 6%, 13)...

or

...+$425 - ($425 - $275)(P/A, 6%, 8) x (A/P, 6%, 13)...