`125-21.8`
`=125-168`
`=-43`
`300:{390-[500-(5^3+49.5)]}`
`=300:{390-[500-(125+245)]}`
`=300:{390-370}`
`=300:20`
`=15`
`3^x` `-2=1`
`->` `3^x` `=1+2`
`->` `3^x` `=3`
`->` `x=1`
$5^{2x-1}$ `-` `3` . $5^{2}$ `=` `2` . $5^{2}$
`->` $5^{2x-1}$ `-` `3` . `25` `=` `2` . `25`
`->` $5^{2x-1}$ `-` `75` `=` `50`
`->` $5^{2x-1}$ `=50+75`
`->` $5^{2x-1}$ `=125`
`->` $5^{2x-1}$ `=5^3`
`->2x-1=3`
`->2x=3+1`
`->2x=4`
`->x=4:2`
`->x=2`
