I'm not getting your answers

a) For the computer:

After year one, the value drops to:

125000 - (125000*0.30) = 87500

After year two, we get 61250

and so on, until year 5, (year 3 = 42875, year 4 = 30012.5)

30012.5 - (30012.5*0.3) = 21008.75

Or use the imple formula,

A_n = P(1-R)^n

A_5 = 125000(1-0.3)^5 = 21008.75

Same thing for the suite.

A_5 = 20000(1+0.06)^5 = 26764.51

As for (b), I'm not so sure, just so you know. I'm using this very same formula, but grouping the costs altogether.

A_5 = P(1 - R)^n

(21008.75 + 26764.51) = (125000+20000)(1 - R)^5

And I get

R = 0.199

R =~ 20%