How do i figure out an equation like this 2 over 3 minus 9/8 if that makes sense

$$\left({\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right){\mathtt{\,-\,}}\left({\frac{{\mathtt{9}}}{{\mathtt{8}}}}\right) = {\mathtt{\,-\,}}{\frac{{\mathtt{11}}}{{\mathtt{24}}}} = -{\mathtt{0.458\: \!333\: \!333\: \!333\: \!333\: \!3}}$$

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