  In this paper, we establish bounds of the Rankin-Selberg $L$-function for
$SL(2)$ using the supnorm of the Eisenstein series and a purely representation
theoretic index over the real group. Consequently, we obtain a subconvexity
bound $L(\frac{1}{2}+ it, f_1 \times f_2) \leq C (1+
|t|)^{\frac{5}{6}+\epsilon}$ for two Maass cusp forms of $SL(2, \mathbb Z)$.
