Step 1 :
After factoring out $ 5t^{3} $ we have:
$$ 5t^{5}-320t^{3} = 5t^{3} ( t^{2}-64 ) $$Step 2 :
Rewrite $ t^{2}-64 $ as:
$$ t^{2}-64 = (t)^2 - (8)^2 $$Now we can apply the difference of squares formula.
$$ I^2 - II^2 = (I - II)(I + II) $$After putting $ I = t $ and $ II = 8 $ , we have:
$$ t^{2}-64 = (t)^2 - (8)^2 = ( t-8 ) ( t+8 ) $$