okay, k, a, b and c are just constants. you treat them as you would any number when finding the derivative or whatever.

(1) We find the maximum of a function by finding it's derivative and setting it equal to zero, so let's do that

f(x) = x + k/x

=> f ' (x) = 1 - k/(x^2)

for max, set f ' (x) = 0

=> 1 - k/(x^2) = 0

=> k = x^2

we want max at x = -2

so k = (-2)^2 = 4