Correct Answer - D
`H_A = H_(Total)`
`:. (TD)_A/R_A = (TD)/(R_A + R_B)`
`:. (TD)_A = ((R_A)/(R_A+R_B)) TD`
`=(1/(1+R_B//R_A)) TD` ……….(i)
`R_B/R_A = (l_B/l_A)(K_AA)/(K_BA) = (20/10)(3) = 6`
Substituting in Eq. (i), we get
`(TD)_A = (1/(1+6)) xx 35 = 5^@C` .