Step-by-step explanation:
[tex] \frac{3a - 1}{4 } - \frac{2a + 1}{7} = 3 \\ \\ \frac{7(3a - 1)}{4 \times 7} - \frac{4(2a + 1)}{7 \times 4} = 3 \\ \\ \frac{(21a - 7)}{28} - \frac{(8a + 4)}{28} = 3 \\ \\ \frac{(21a - 7) - (8a + 4)}{28} = 3 \\ \\ \frac{21a - 7 - 8a - 4}{28} = 3 \\ \\ \frac{13a - 11}{28} = 3 \\ \\ 13a - 11 = 28 \times 3 \\ \\ 13a - 11 = 84 \\ \\ 13a = 84 + 11 \\ \\ 13a = 95 \\ \\ a = \frac{95}{13} \\ \\ \huge \red{ \boxed{ a = 7 \frac{4}{13}}} [/tex]
