Factorise this:

e^-0.4 *t +2e^0.4t
Im not sure how to factorise this

Not sure with your inconsistent typing

I will assume you meant
e^(-.4t) + 2 w^(.4t) , don't know why you typed the exponents in different ways
= e^(-.4t) (1 + 2 e^(.8t) )

(if you have powers with the same base, in this case the base is e,
then take out the power with the smaller exponent as a common factor)

If you meant it the way you typed it, there is very little that can be done