2 x ( X + 56 ) - 13 = 780
2 x ( X + 56 ) = 793
X + 56 = 396,5
X = 340,5
\(2.\left(x+56\right)-13=65.12\)
\(2.\left(x+56\right)-13=780\)
\(2.\left(x+56\right)=780+13\)
\(2.\left(x+56\right)=793\)
\(\left(x+56\right)=793:2\)
\(x+56=396,5\)
\(x=396,5-56\)
\(x=340,5\)
Vậy \(x=340,5\)