`a, 66:0,33+3,06-0,05xxx=202,86`
`200 + 3,06 - 0,05 × x = 202,86`
`203,06 - 0,05 × x = 202,86`
`0,05 × x = 203,06 -202,86`
`0,05×x=0,2`
`x = 0,2 : 0,05`
`x = 4`
`b, 4 × x + 18 × x 2 × x = 47928`
`(4 + 18 + 2) × x = 47928`
`24 × x = 47928`
`x = 47928 : 24`
`x=1997`
`c, (400:x)×3 = 75`
`400:x = 75 : 3`
`400:x = 25`
`x= 400 : 25`
`x = 16`