Limits of real fn jee qn

Question

let n ∑ r = 1 r ^4/ ( 2 r − 1 ) ( 2 r + 1 ) = n^3/ a + n ^2/ b + 5 n/ c + f ( n ) /d. ( a , b , c , d ∈ n ) where f(n) is the ratio of two linear polynomials such that lim n → ∞ f ( x ) = 1/2 . find the value of ( a + b + c + d ) .