Another way of writing it is: (k * k *k) + ((3 * K) * (3 * K))

k^3 can be read as "k cubed" or "k to the 3rd power" k^2 can be read as "k squared" or "k to the 2nd power" Thus I would read it as "k cubed plus 3 k squared". There are a couple acceptable alternatives that are equally as correct. You could also say "3 times k" instead of simply "3k".