`(42,5-x)xx6,5=87,1`
`=>42,5-x=87,1:6,5`
`=>42,5-x=13,4`
`=>x=42,5-13,4`
`=>x=29,1`
Vậy `x=29,1`
\(\left(42,5-x\right)\times6,5=87,1\)
\(\Leftrightarrow42,5-x=87,1:6,5\)
\(\Leftrightarrow42,5-x=13,4\)
\(\Leftrightarrow x=42,5-13,4\)
\(\Leftrightarrow x=29,1\)