Đáp án đúng: C
Giải chi tiết:\(\begin{array}{l}\,\,\,\,28:\left( {x + 1} \right) = 7\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x + 1\,\,\, = 28:7\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x + 1\,\,\, = 4\\\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x\,\,\,\,\,\,\,\,\,\, = 3\end{array}\)
Chọn C