I assume that the first one is :
lim x → −∞ 4e^x = 0
Note that, as x → −∞, e^x will grow smaller and smaller.....and if we let x assume some large negative value, e^x, will approach 0
Therefore,
lim x → −∞ 4e^x = 0
Likewise, I assume that the second one is :
lim x → ∞ 2e^x = ∞
Again, if we let x approach some large positive value, e^x will grow larger and larger. So, as x → ∞ , e^x will also approach ∞
Here's the graph of e^x that will give you some idea of the end behaviors of both functions :
https://www.desmos.com/calculator/ml0aj0en2z
