`a, x xx 5 + 122 + 236 = 633`

`x xx 5 + 358 = 633`

`x xx 5 = 633 - 358`

`x xx 5 = 275`

`x = 275 : 5`

`x = 55`

`b, ( x : 12 ) xx 7 + 8 = 36`

`( x : 12 ) xx 7 = 36 - 8`

`( x : 12 ) xx 7 = 28`

`x : 12 = 28 : 7`

`x : 12 = 4`

`x = 4 xx 12`

`x = 48`