`a,( x ÷ 7 - 7 )( x ÷12 - 12) = 0`
`⇔` \(\left[ \begin{array}{l}x÷7-7=0\\x÷12-12=0\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x÷7=7\\x÷12=12\end{array} \right.\)
`⇔` \(\left[ \begin{array}{l}x=49\\x=144\end{array} \right.\)
$b,140 - 100 ÷ x = 120$
`140 - 120 = 100 ÷ x`
`100 ÷ x = 20`
`100 ÷ 20 = x`
`⇒ x = 5`
`c,x ÷ 3 - 13 = 47`
`x ÷ 3 = 47 + 13`
`x ÷ 3 = 60`
`x = 60 × 3`
`x = 180`
`d,135 + x ÷ 2 = 150`
`x ÷ 2 = 150 - 135`
`x ÷ 2 = 15`
`x = 15 × 2`
`x = 30`
`e,300 - x ÷ 5 = 273`
`300 - 273 = x ÷ 5`
`x ÷ 5 = 27`
`x = 27 × 5`
`x = 135`
$@Race2k53$
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