(F – 1) = 8 (s – 1) ∴ F – 1 = 8s – 8 ∴ 8s – F = 7 ...(i) Now, F = s2 , putting this value in eq. (i) 8s – s2 = 7 or s2 – 8s + 7 = 0 or s2 – s – 7s + 7 = 0 or s(s – 1) – 7 (s – 1) = 0 or (s – 7) (s – 1) = 0 ∴ s =7 or 1 But it could not be 1 yr because then it will not fulfill the conditions. ∴ s = 7