  Calculations of pseudoscalar decay constants of B, Bs, K and pi mesons with
physical light quarks are presented. We use HISQ ensembles that include u,d,s
and c sea quarks at three lattice spacings. HISQ is used for the valence light
quarks and a radiatively improved NRQCD action for the heavy quarks. The key
results are f_{B^+}=0.184(4)$ GeV, f_{B_s}=0.224(4) GeV,
f_{B_s}/f_{B^+}=1.217(8), f_{K^+}/f_{pi^+}=1.1916(21), f_{K^+}=155.37(34) MeV,
giving a significant improvement over previous results that required chiral
extrapolation. We also calculate the Wilson flow scale w_0, finding
w_0=0.1715(9) fm.
