75% x X + 3/4 x X +X=30
3/4 x X +3/4 x X + X =30
X x (3/4 +3/4 +1)=30
X x (3/2 +1)=30
X x 5/2 = 30
X = 30 : 5/2
X = 30x2/5
X = 12
Ta có: \(75\%\cdot x+\dfrac{3}{4}\cdot x+x=30\)
\(\Leftrightarrow\dfrac{3}{4}\cdot x+\dfrac{3}{4}\cdot x+x=30\)
\(\Leftrightarrow\dfrac{5}{2}\cdot x=30\)
\(\Leftrightarrow x=30:\dfrac{5}{2}=30\cdot\dfrac{2}{5}=12\)
Vậy: x=12