`12 : x . 5 + 10 = 30`
`<=> 12 : x . 5 = 20`
`<=> 12 : x = 20 : 5 = 4`
`<=> 12 : x = 4`
`<=> x = 3`
-------------------------------------
`x - 2^2 . 5 = 10`
`<=> x - 4.5=10`
`<=> x - 20 = 10`
`<=> x = 10 + 20`
`<=> x = 30`
-------------------------------------------
`27 : 3^2 + x = 10`
`<=> 27 : 9 + x = 10`
`<=> 3 + x = 10`
`<=> x = 10 - 3`
`<=> x = 7`
--------------------------------------------
`16 : x . 5 + 10 = 20`
`<=> 16 : x . 5 = 10`
`<=> 16 : x = 10 : 5`
`<=> 16 : x = 2`
`<=> x = 8`
-----------------------------------------------
`(46 - x) : 9 - 4 = 1`
`<=> (46 - x) : 9 = 5`
`<=> 46 - x = 5 . 9`
`<=> 46 - x = 45`
`<=> x = 1`
