I have the answers to the questions, however I need help with solving them.

a$)=18\%$

b$)=20\%$

c$)=$r$=103\mathrm{.}9$ ohm

d$)=$Ro$=0\mathrm{.}844$ ohm$$m

e$)=$Sw$=40\%$

f$)=$r$=520$ ohm, $5\mathrm{.}28$ ohm$$m