Two $50$ Hz generating units operate in parallel within the same plants, with the following ratings:

Unit $1$: $500$MVA,$13\mathrm{.}2kV,0\mathrm{.}8pf,3600rpm$:$H=4M\frac{J}{M}VA.$

Unit $2$: $1000$MVA,$13\mathrm{.}8kV,0\mathrm{.}9pf,1800rpm$:$H=5M\frac{J}{M}VA.$

Find the equivalent H constant on a base of $100$ MVA $.$