Answer
$$\left[\begin{array}{ccc}{1} & {1} \\ {1} & {\frac{3}{2}}\end{array}\right].$$
Work Step by Step
Let $$
A=\left[\begin{array}{ccc}{1} & {2} \\ {3} & {4}\end{array}\right], \quad B=\left[\begin{array}{ccc}{-1} & {0} \\ {1} & {1}\end{array}\right].
$$
We have
$$2X=A-B\Longrightarrow X=\frac{1}{2}(A-B)=\frac{1}{2}A-\frac{1}{2}B$$
and hence $$X=\frac{1}{2}\left[\begin{array}{ccc}{1} & {2} \\ {3} & {4}\end{array}\right]-\frac{1}{2}\left[\begin{array}{ccc}{-1} & {0} \\ {1} & {1}\end{array}\right]=\left[\begin{array}{ccc}{1} & {1} \\ {1} & {\frac{3}{2}}\end{array}\right].$$
