Solve for $c$. \[ a=\frac{1}{8}(b+c-d) \]

Step 1 ：Multiply both sides of the equation by 8 to get rid of the fraction: \(8a = b + c - d\)

Step 2 ：Add d to both sides of the equation: \(8a + d = b + c\)

Step 3 ：Subtract b from both sides of the equation: \(8a + d - b = c\)

Step 4 ：\(\boxed{c = 8a - b + d}\)