$\text { Đáp án: }$
` 1/3 - x = 5/7 + 2 1/4 `
` => 1/3 - x = 5/7 + 9/4 `
` => 1/3 - x = 20/28 + 63/28 `
` => 1/3 - x = 83/28 `
` => x = 1/3 - 83/28 `
` => x = 28/84 - 249/84 `
` => x = –221/84 ` ` (= –2 57/84) `
$\text { Vậy }$ ` x = –221/84 ` ` (= –2 57/84) `