4/25 + x/13 =0,76
=> x/13 = 0,76 -4/25
=> x/13 = 0,6
=> x = 0,6 x 13
=> x = 7,8
\(\frac{4}{25}+\frac{x}{13}=0,76\Leftrightarrow\frac{x}{13}=\frac{19}{25}-\frac{4}{25}=\frac{3}{5}\Leftrightarrow x=\frac{3.13}{5}=\frac{39}{5}\)
\(15.x+15.2,7=105\Leftrightarrow15.\left(x+2,7\right)=105\Leftrightarrow x+2,7=7\Leftrightarrow x=7-2,7=4,3\)