When they say to solve for c, they just want you to isolate it. We can start by subtracting b from both sides to give us:
x - b = cd
After this, we can divide both sides by -d to finish isolating the variable c; remember that -cd is -1(c)(d):
[tex]\frac{x-b}{-d}[/tex] = c
Therefore, c = [tex]\frac{x-b}{-d}[/tex]
