[tex]14a + 28c = 7 \\ \\ 14(a + 2c) = 7 \\ \\ a + 2x = \frac{7}{14} \\ \\ a + 2c = \frac{1}{2} \\ \\ 2c = \frac{1}{2} - a \\ \\ c = \frac{ \frac{1}{2} -a}{2} \\ \\ c = \frac{ \frac{1}{2} }{2} - \frac{a}{2} \\ \\ c = \frac{1}{2 \times 2} - \frac{a}{2} \\ \\ c = \frac{1}{4} - \frac{a}{2} \\ \\ Answer: \fbox {c = 1/4 - a/2} [/tex]
