Nucleus $A$ having $Z=17$ and equal number of protons and neutrons has $1.2 \mathrm{MeV}$ binding energy per nucleon. Another nucleus $B$ of $Z=12$ has total $26$ nucleons and $1.8 \mathrm{MeV}$ binding energy per nucleons. The difference of binding energy of $B$ and $A$ will be ______ $\mathrm{MeV}$.