Which is the range of the function y=4e^x

Range ⇒ Values that can 'come out' of the function.

As x → -∞, y → 0
As x → +∞, y → ∞

This means that the smallest value that can come out of the function is a value which is tiny but greater than 0 and the largest is ∞ so the range is option 1, all real numbers greater than 0.

(When I get these questions it always helps me to think of the graph to work out what y approaches as x approaches -∞ and +∞)

Ithink if im not mistaking b is -3 but im not a 100% sude