Answer:
k=20
Step-by-step explanation:
when x approaches 4, the denominator x-4 approaches 0
if the denominator is 0, it means that this is invalid
if the function is a number over 0 when x=4, it represents a vertical asymptote, which means no limit
so the only way possible to let there be a limit is to let the function be 0/0 when we plug in x=4
so x^2 + x - k = 0 when x = 4
4^2 + 4 - k = 0 ==> 20 - k = 0 ==> k = 20
