a: =>x+25=35
=>x=10
b: =>3x-42=3x8=24
=>3x=66
=>x=22
c: =>5x=35
=>x=7
`56 - ( 25+x ) = 21`
`25+x = 56 -21 =35`
`x = 35-25=10`
Vậy `x=10`
`3x-42 =3*2^3`
`3x-42 = 3*8=24`
`3x =24+42 =66`
`x = 66/3 = 22`
Vậy `x=22`
`3x + 2x = 35`
`x(3+2) =35`
`5x=35`
`x =35/5 =7`
Vậy `x=7`
56-(25+x)=21
=>25+x=56-21
=>25+x=35
=>x=35-25
=>x=10
Vậy x=10
3x-42=3×2^3
=>3x-42=3×8
=>3x-42=24
=>3x=24+42
=>3x=66
=>x=66÷3
=>x=22
Vậy x=22