Tìm (x), biết:

a) \(2 + x:5 = 6\)

\(x:5 = 4\)

\(x = 20\)

Vậy \(x = 20\).

b) \( - 152 - \left( {3x + 1} \right) = 54\)

\[3x + 1 =  - 152 - 54\]

\[3x + 1 =  - 206\]

\(3x =  - 207\)

\(x =  - 69\)

Vậy \(x =  - 69\).

c) \({5.3^{x - 1}} + {3^{x - 1}} = 162\)

\[{3^{x - 1}}.\left( {5 + 1} \right) = 162\]

\[{3^{x - 1}}.6 = 162\]

\[{3^{x - 1}} = 27\]

\({3^{x - 1}} = {3^3}\)

Suy ra \(x - 1 = 3\)

\(x = 4\)

Vậy \(x = 4\).