Tìm x, biết: \(30\% x + \frac{1}{4}x + 89 = 100\).

\(30\% x + \frac{1}{4}x + 89 = 100\)

\(\left( {\frac{3}{{10}} + \frac{1}{4}} \right)x + 89 = 100\)

\(\frac{{11}}{{20}}x = 100 - 89\)

\(\frac{{11}}{{20}}x = 11\)

x = 20

Vậy x = 20.