1. $N$
2. $N$
4. $N$

5. $$\color{blue}{\rightarrow}\color{black}\;N \;= \;\frac{A_B}{\lambda}$$

   $$\color{blue}{\rightarrow}\color{black}\;N \;= \;\frac{A_C\cdot 3,7\cdot 10^{10}}{\lambda}$$

   $$\color{blue}{\rightarrow}\color{black}\;N \;= \;\frac{A_B\cdot T_{1/2}}{ln\,2}$$

   $$\color{blue}{\rightarrow}\color{black}\;N \;= \;\frac{A_C\cdot T_{1/2}\cdot 3,7\cdot 10^{10}}{ln\,2}$$

1. $\lambda$
2. $\lambda$
4. $\lambda$

5. $$\color{blue}{\rightarrow}\color{black}\;\lambda\;= \;\frac{ln2}{T_{1/2}} $$

1. $T_{1/2}$
2. $T_{1/2}$
4. $T_{1/2}$

5. $$\color{blue}{\rightarrow}\color{black}\;T_{1/2}\;= \;\frac{ln2}{\lambda} $$

1. $A_B$
2. $A_B$
4. $A_B$

5. $$\color{blue}{\rightarrow}\color{black}\;A_B\;= \;N\cdot \lambda $$

   $$\color{blue}{\rightarrow}\color{black}\;A_B\;= \;\frac{N\cdot ln\,2} {T_{1/2}} $$

1. $A_C$
2. $A_C$
4. $A_C$

5. $$\color{blue}{\rightarrow}\color{black}\;A_C\;= \;\frac{N\cdot \lambda}{3,7\cdot 10^{10}} $$

   $$\color{blue}{\rightarrow}\color{black}\;A_C\;= \;\frac{N\cdot ln\,2} {3,7\cdot 10^{10}\cdot T_{1/2}} $$

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If you want to introduce for example $1,6\cdot 10^{-9}$ type 1.6E-9