Javier and his friends go out to eat. The restaurant they chose automatically adds a 15% gratuity to their food bill since they are a party of 12. The total bill after the automatic 15% gratuity was $213.90. Because they received such good service, the group decided to add an extra $20 to the total bill as an additional tip. So, instead of leaving a 15% tip, Javier and his friends ended up leaving a tip that was about % of the food bill.

well, we know that 213.90 includes the 15% gratuity, so if the meal price was say "x", namely that is the 100%, and we add 15% to that, then 100% + 15% = 115%, so 213.90 is really the 115%.now, if 213.90 is the 115.%, what is "x"?  the 100%.
[tex]\bf \begin{array}{ccll} amount&\%\\ \cline{1-2} 213.90&115\\ x&100 \end{array}\implies \cfrac{213.9}{x}=\cfrac{115}{100}\implies 21390=115x \\\\\\ \cfrac{21390}{115}=x\implies 186=x[/tex]
so since we know the meal without the tip is 186 bucks, the tip was then 213.90 - 186 = 27.90.but they got extra potato wedges with butter and the waitress was wearing her best hat, they added $20 more, so the tip ended  up as 27.90 + 20 = 47.90.now, if the cost of the meal was $186 and that is the 100%, what is 47.90 off of it in percentage?
[tex]\bf \begin{array}{ccll} amount&\%\\ \cline{1-2} 186&100\\ 47.90&x \end{array}\implies \cfrac{186}{47.90}=\cfrac{100}{x}\implies 186x=4790 \\\\\\ x=\cfrac{4790}{186}\implies x\approx \stackrel{\%}{25.75}[/tex]