jmc

Multiplying by 5 gives $|9+2a|<5$, so we must have $$-5<9+2a<5.$$Subtracting 9 from all three parts of this inequality chain gives $$-14<2a<-4,$$and dividing by 2 gives $-7<a<-2,$ or $a\in \boxed{(-7,-2)}$ in interval notation.