Aloha :)$$\left.c=\frac{4+w}{w+3}=\frac{w+\overbrace{3+1}^{=4}}{w+3}=\frac{w+3}{w+3}+\frac{1}{w+3}=1+\frac{1}{w+3}\quad\right|\;-1$$$$\left.c-1=\frac{1}{w+3}\quad\right|\;\text{Kehrwert}$$$$\left.\frac{1}{c-1}=w+3\quad\right|\;-3$$$$w=\frac{1}{c-1}-3$$