Bài làm :
Ta có :
\(...\Leftrightarrow390-x+7=13\Leftrightarrow397-x=13\Leftrightarrow x=397-13=384\)
Vậy x=384
GIẢI
390-(X-7)=13
(X-7)=390-13
X=377-7
X=370
\(390-\left(x-7\right)=13^2:13\)
\(390-\left(x-7\right)=13\)
\(x-7=390-13\)
\(x-7=377\)
\(x=377+7\)
\(x=384\)