I can show you a couple different "ways" of doing it. (They all accomplish the same thing though.)
\(x - \frac{80}{100} = 90 \\~\\ x=90+\frac{80}{100} \\~\\ x=\frac{454}{5}=90.8\)
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\(x - \frac{64}{100} = 72 \\~\\ x-0.64=72 \\~\\ x=72+0.64=72.64\)
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\(x - 15\% = 146.54 \\~\\ x - 0.15 = 146.54 \\~\\ x = 146.54 + 0.15 =146.69\)
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