[tex] \frac{a + b + c}{3} = 12.6 \\ c = 2a \\ b = a + 2.1 \\ \\ \frac{a + a + 2.1 + 2a}{3} = 12.6 \\ \frac{4a + 2.1}{3} = 12.6 \\ \frac{4a + \frac{21}{10} }{3} = 12.6 \\ \frac{ \frac{40a + 21}{10} }{3} = 12.6 \\ \frac{40a + 21}{10} \times \frac{1}{3} = 12.6 \\ \frac{40a + 21}{30} = 12.6 \\ 40a + 21 = 12.6 \times 30 \\ 40a + 21 = 378 \\ 40a = 357 \\ a = 357 \div 40 = 8.925[/tex]
a=8.925
b=a+2,1
b=8,925+2,1
b=11,025
c=2a
c=2×8,925
c=17,85
