Current amount of gas: [tex]\frac{1}{10} t[/tex]
After adding 11 gallons: [tex]\frac{1}{10} t[/tex] + 11 = [tex]\frac{3}{5} t[/tex]
11 = [tex]\frac{3}{5} t[/tex] - [tex]\frac{1}{10} t[/tex]
11 = [tex]\frac{6}{10} t[/tex] - [tex]\frac{1}{10} t[/tex]
11 = [tex]\frac{5}{10} t[/tex]
11 = [tex]\frac{1}{2} t[/tex]
22 = t
Answer: 22 gallons
