Multiplying a matrix by a scalar is very simple: you only have to multiply every entry of the matrix by that scalar.
So, we have
[tex]A=\left[\begin{array}{cc}-\dfrac{4}{3}&-5\\-2&-4\end{array}\right]\implies -\dfrac{1}{2}A=\left[\begin{array}{cc}-\dfrac{1}{2}\left(-\dfrac{4}{3}\right)&-\dfrac{1}{2}(-5)\\-\dfrac{1}{2}(-2)&-\dfrac{1}{2}(-4)\end{array}\right]=\left[\begin{array}{cc}\dfrac{2}{3}&\dfrac{5}{2}\\1&2\end{array}\right][/tex]
