25-x/40=3/8
=>25-x= 3/8x40
=>25-x=15
=>x=25-15
=>x=10
20-x /40 =3/8
=>20-x= 3/8 x40
=>20-x=15
=>x=20-15
=>x=5
20-x /40 =3/8
=>20-x= 3/8 x40
=>20-x=15
=>x=20-15
=>x=5
20-x /40 =3/8
=>20-x= 3/8 x40
=>20-x=15
=>x=20-15
=>x=5
\(\frac{25-x}{40}=\frac{3}{8}\)
\(\Leftrightarrow8\left(25-x\right)=3.40\)
\(\Leftrightarrow200-8x=120\)
\(\Leftrightarrow-8x=120-200\)
\(\Leftrightarrow x=10\)