$$ \begin{aligned} \frac { 8-h }{ 20-2x } &= \frac { 8 }{ 20 } \\\,\\ \frac { 8-h }{ 8 } &= \frac { 20-2x }{ 20 } \\\,\\ \frac { -h }{ 8 } &= \frac { -2x }{ 20 } \\\,\\ h &= -\frac { 4 }{ 5 }x. \\\,\\ \text{Korrektur: } h &= \frac { 4 }{ 5 }x. \end{aligned} $$