[tex]\bf \cfrac{4^2-20\div 5}{1-5+7}\implies \cfrac{\stackrel{\downarrow }{16}-20\div 5}{1-5+7}\implies \cfrac{16-\stackrel{\downarrow }{4}}{1-5+7}\implies \cfrac{\stackrel{\downarrow }{12}}{1-5+7} \\\\\\ \cfrac{12}{\stackrel{\downarrow }{-4}+7}\implies \cfrac{12}{\stackrel{\downarrow }{3}}\implies 4[/tex]
