180+p\%*180=180(1+p\%)=180(100\%+p\%)=180(\frac{100}{100}+\frac{p}{100})=180(\frac{100+p}{100})
m-n\%m=m(1-n\%)=m(100\%-n\%)=m(\frac{100}{100}-\frac{n}{100})=m(\frac{100-n}{100})
40000-x\%*40000=a
40000(1-x\%)=a
1-x\%=\frac{a}{40000}
-x\%=\frac{a}{40000}-1
x\%=-\frac{a}{40000}+1
x\%=1-\frac{a}{40000}
\frac{x}{100}=1-\frac{a}{40000}
x=(1-\frac{a}{40000})*100