If nC r - 1 = 36, nC r = 84 and nC r + 1 = 126 then?

ⁿC_{r - 1} = 36, ⁿC_r = 84 and ⁿC_{r + 1} = 126
⇒ ⁿC_r / ⁿC_{r - 1} = 84/36
⇒ 3n - 10r + 3 = 0 ....(i)
ⁿC_{r + 1} / ⁿC_r = 126/84
⇒ 2n - 5r - 3 = 0 .............(ii)
From (i) and (ii) r = 3, n = 9