We have got an geometric progression.
We use to find any term of a geometric sequence, this equation:
an=a₁ * r^(n-1)
a₁= is the first term.
r=is the common ratio.
n=numbers of the term to find.
r=an / an-1
In this case:
r=a₂/a₁=(-4.8) / 9.6=-0.5
a₁=9.6
an=9.6*(-0.5)^(n-1)