\(a,m_{NaCl}=\dfrac{200.10}{100}+10=30\left(g\right)\\ m_{dd}=200+10=210\left(g\right)\\ C\%_{NaCl}=\dfrac{30}{210}.100\%=14,29\%\\ b,m_{NaCl}=50.5\%+200.10\%=22,5\left(g\right)\\ m_{dd}=200+50=250\left(g\right)\\ C\%_{NaCl}=\dfrac{22,5}{250}.100\%=9\%\)