[tex]57 - 8 \times 3 + 2 \times (10 - 6) + a \times 3 = 50 \\ \\ 57 - 24 + 2 \times 4 + a \times 3 = 50 \\ \\ 57 - 24 + 8 + a \times 3 = 50 \\ \\ 33 + 8 + a \times 3 = 50 \\ \\ 41 + 3a = 50 \\ \\ 3a = 50 - 41 \\ \\ 3a = 9 \\ \\ a = 9 \div 3 \\ \\ a = 3[/tex]
