`a``)` `x``+``30` `:` `2``=``150`
`x``+` `15``=``150`
`x``=``150``-``15`
`x``=``135`
`b``)` $5^{x+1}$ `+``5``=``150`
$5^{x}$`.``5` `+``5``=``150`
`5``.``(`$5^{x}$`+``1``)``=``150`
$5^{x}$`+``1``=``150` `:` `5`
$5^{x}$`+``1``=``30`
$5^{x}$`=``30``-``1`
$5^{x}$`=``29`
⇒ Không tìm được x.