In view of recent measurements of anomalies in semileptonic B-meson decays at several collider experiments hinting at the possible violation of lepton-flavor universality, we have undertaken a review of theoretical foundations of the tree- and loop-level b decays along with the experimental background. We revisit the world averages in the updated environment for $R_{\mathrm{D}(\mathrm{D}^*)}$, $R_{\mathrm{K}(\mathrm{K}^*)}$, $R_{\mathrm{J}/\psi}$ and $R_{\eta_{\text{c}}}$, in a model dependent as well as independent approach and have provided the results. Further predictions of other anomalies in view of future high-statistics data are also discussed. A confirmation of these measurements would soon turn out to be the first observation of physics beyond the Standard Model giving a wider outlook on the better understanding of New Physics.