[tex] p\%=\dfrac{p}{100}\to 75\%=\dfrac{75}{100}=0.75\\\\n-the\ number\\\\the\ equation:\\\\n+0.75n=80\\\\1.75n=80\ \ \ \ |:1.75\\\\n=\dfrac{80\cdot100}{1.75\cdot100}\\\\n=\dfrac{8000}{175}\\\\n=\dfrac{8000:25}{175:25}\\\\n=\dfrac{320}{7}\\\\n=45\dfrac{5}{7} [/tex]
