`Câu 1:`
`165 - (35 : x + 3) . 19 = 13`
`(35 : x + 3) . 19 = 165 - 13`
`(35 : x + 3) . 19 = 152`
`35 : x + 3 = 152 : 19`
`35 : x + 3 = 8`
`35 : x = 8 - 3`
`35 : x = 5`
`x = 35 : 5`
`x = 7`
`⇒ A`
`Câu 2:`
`5(x + 15) = 5^3`
`x + 15 = 5^3 : 5`
`x + 15 = 5^2`
`x + 15 = 25`
`x = 25 - 15`
`x = 10`
`⇒ B`
`Câu 3:`
`2 . 10^3 + 7 . 10^2`
`= 2. 10 . 10^2 + 7 . 10^2`
`= (20 + 7) . 10^2`
`= 27 . 100`
`= 2700`
`⇒ `ko có đáp án