Aus Online Mathematik Brückenkurs 1

The first step is to expand the fractions so that they have a common denominator,

\displaystyle \frac{8\cdot 4\cdot 3}{7\cdot 4\cdot 3}+\frac{3\cdot 7\cdot 3}{4\cdot 7\cdot 3}-\frac{4\cdot 7\cdot 4}{3\cdot 7\cdot 4}=\frac{96}{84}+\frac{63}{84}-\frac{112}{84}\,.

After that, the expression can be calculated by adding and subtracting the numerators

\displaystyle \frac{96}{84}+\frac{63}{84}-\frac{112}{84}=\frac{96+63-112}{84}=\frac{47}{84}\,.