Answer:
[tex]4c + 9d = 16 \\ 4c = 16 - 9d \\ \\ c = \frac{16 - 9d}{4} \\ \\ c = \frac{16}{4} - \frac{9d}{4} \\ \\ \\ c = 4 - \frac{9d}{4} [/tex]
I hope I helped you^_^