Question

18/ a +23=3/5 4/7=8+2a/21

Answer 1

1.
$\frac{18}{a} = \frac{3}{5} - 23 \\ \frac{18}{a} = - \frac{122}{5} \\ 90 = - 122a \\ - 122a = 90 \\ a = - \frac{45}{56}$
2.
4/5=8+2а/21
12=168+2а
-2а =156
а=-78

Answer 2

I'm sorry, your question is not clear. It seems like you have provided two equations, but there are no instructions or a question for me to solve or simplify them. Can you please provide more information or clarify your question?