30 -(\(x\) - 4) = 10
\(x-4\) = 30 - 10
\(x\) - 4 = 20
\(x\) = 20 + 4
\(x\) = 24
b, 75% : \(x\) = 3\(\dfrac{1}{2}\) - 1\(\dfrac{1}{2}\)
75% : \(x\) = \(\dfrac{7}{2}\) - \(\dfrac{3}{2}\)
75% : \(x\) = \(\dfrac{4}{2}\)
75% : \(x\) = 2
\(x\) = 75% : 2
\(x\) = 37,5%