а) \( 3a-1 + \frac{9+6}{129} \) = \( \frac{(3a-1)129 + 9+6}{129} \) = \( \frac{387a-129+15}{129} \) = \( \frac{387a-114}{129} \)
б) \( 6x-y - \frac{20-44}{1400} \) = \( \frac{(6x-y)1400 - 20+44}{1400} \) = \( \frac{8400x-1400y+24}{1400} \) = \( \frac{2100x-350y+6}{350} \)
Ответ: а) \( \frac{387a-114}{129} \), б) \( \frac{2100x-350y+6}{350} \)