[tex] \: (70 - a) \times 2 + 20 = \\ ( \frac{80}{3} + 5a) \times 2 + 20[/tex]
[tex] - 5a - a = 70 - \frac{80}{3}[/tex]
[tex] - 6a = - \frac{52}{3}[/tex]
[tex]a = - \frac{52}{3} \times - \frac{1}{6} [/tex]
[tex]a = + \frac{52}{18} [/tex]
[tex]a = \frac{26}{9} [/tex]