Упростим уравнение:
\(k - \frac{2}{5}k = 4,5\)
\(\frac{5}{5}k - \frac{2}{5}k = 4,5\)
\(\frac{3}{5}k = 4,5\)
\(k = 4,5 : \frac{3}{5} = 4,5 \cdot \frac{5}{3} = \frac{4,5 \cdot 5}{3} = \frac{22,5}{3} = 7,5\)
Ответ: \(k = 7,5\)