a) $\frac{14\times50+43\times100}{26\times96+142\times48}=\frac{14\times50+43\times2\times50}{26\times2\times48+142\times48}=\frac{14\times50+86\times50}{52\times48+142\times48}=\frac{(14+86)\times50}{(52+142)\times48}=\frac{100\times50}{194\times48}=\frac{625}{1164}$
b) $\frac{299\times45+55\times299}{2019\times2020-2015\times2019}=\frac{299\times(45+55)}{2019\times(2020-2015)}=\frac{299\times100}{2019\times5}=\frac{299\times20}{2019}=\frac{5980}{2019}$