$\displaystyle k-\left( \frac{1}{3} \cdot k+3 \right)$\displaystyle k-\left( \frac{1}{3} \cdot k+3 \right)

$\displaystyle \frac{1}{3} \cdot k-3$\displaystyle \frac{1}{3} \cdot k-3

$\displaystyle k- \frac{1}{3}-3$\displaystyle k- \frac{1}{3}-3

$\displaystyle \displaystyle k-\left( \frac{1}{3} \cdot k-3 \right)$\displaystyle \displaystyle k-\left( \frac{1}{3} \cdot k-3 \right)