I will try to help.
Lim x → −∞ 4e^x=0
because you can change it to look like
Lim x → ∞ 4/e^x
Then the denominator gets big so it goes to zero
But listen to the BIG BOSS first. I am trying to help, so I may be incorrect. CPhill, the class genius, will tell you the answer, and maybe correct me.