`a) 120 + [ 9 . ( 111 - x ) : 60 ] . 24 = 480`
`[9 . (111 - x) : 60] . 24 = 480 - 120`
`[9. (111 - x) : 60] . 24 = 360`
`9. (111 - x) : 60 = 360 : 24`
`9. (111 - x) : 60 = 15`
`9. (111 - x) = 15 . 60`
`9. (111 - x) = 900`
`111 - x = 900 : 9`
`111 - x = 100`
`x = 100 - 111`
`x = 11`
`b) 720 : [ 41 - ( 2x + 5 ) ] = 8 . 8`
`720 : [41 - (2x + 5)] = 64`
`41 - (2x + 5) = 720 : 64`
`41 - (2x + 5) = 11,25`
`2x + 5 = 41 - 11,25`
`2x + 5 = 29,75`
`2x = 29,75 - 5`
`2x = 24,75`
`x = 24,75 : 2`
`x = 12,375`
`c) ( 2x - 130 ) : 4 + 213 = 44`
`(2x - 130) : 4 = 44 - 213`
`(2x - 130) : 4 = - 169`
`2x - 130 = (- 169) xx 4`
`2x - 130 = - 676`
`2x = (-676) + 130`
`2x = - 546`
`x = (-546) : 2`
`x = - 273`
`d) ( 2x + 5 ) . ( 2x + 5 ) . ( 2x + 5 ) . 9 + 9 = 72`
`(2x + 5) . (2x + 5) . (2x + 5) . 9 = 72 - 9`
`(2x+ 5) . (2x + 5) . (2x + 5) . 9 = 63`
`(2x + 5) . (2x + 5) . (2x + 5) = 63 : 9`
`(2x + 5). (2x + 5) . (2x + 5) = 7`
`(2x + 5)^3 = 7`
`=> x ∈ ∅`
