Tìm số tự nhiên x , biết:

a)\(135 + 5.x = 625\)

 \(\begin{array}{l}5x = 625 - 135\\5x = 490\\x = 98\end{array}\)

Vậy \(x = 98\).

 b)\[196 - 3.\left( {x + 8} \right) = {4^9}:{4^7}\]

 \(\begin{array}{l}196 - 3.\left( {x + 8} \right) = {4^2}\\196 - 3.\left( {x + 8} \right) = 16\end{array}\)

\(3.\left( {x + 8} \right) = 180\)

\(\begin{array}{l}x + 8 = 60\\x = 52\end{array}\)

Vậy\(x = 52\).