$@Shin$
Câu 1 : $\dfrac{3}{x}$ = $\dfrac{2}{5}$
→ `2x` = `3.5`
→ `2x` = `15`
→ `A`. `x` = $\dfrac{15}{2}$
Câu 2 : $\dfrac{-3,8}{x}$ = $\dfrac{0,26}{0,39}$
→ `0,26x` = `-3,8.0,39`
→ `0,26x` = `-1,482`
→ `B` . `x` = `-5,7`
Câu 3 : $\dfrac{a}{b}$ = $\dfrac{c}{d}$
→ `D` = $\dfrac{b}{a}$ = $\dfrac{d}{c}$