the two brackets (a+2) will cancel out each other to give...
(1 / (a^2 + a)) ÷ (1/(a^3)
then if we multiply both the top line and the bottom line by a^3 then the (1/(a^3)) bit we originally have will disappear as
a^3/a^3 is 1
multiply (1 / (a^2 + a)) by a^3 we get (a^3)/(a^2 + a)
this is effectively turning the divisor upside down and multiplying.
now (a^2 + a) can be factorised into what...?