Tìm X [ X - 21 x 13 ] : 11 = 39

`\text{(X - 21 × 13 ) ÷ 11 = 39}`

`\text{X - 21 × 13 = 39 × 11}`

`\text{X - 21 × 13 = 429}`

`\text{X - 21 = 429 ÷ 13}`

`\text{X - 21 = 33}`

`\text{X = 33 + 21}`

`\text{⇒ X = 54}`