This looks like a system of equations:
We should solve for c on the first equation because we can substitute for c. There are a lot of ways we can do a system of equations, but I will do this.
c - 3d = 11
+3d +3d
c = 11 +3d
Now we can substitute.
-2(11+3d) + 3d = -16
solve
-22 + -6d + 3d = -16
-22 + -3d = -16
+22 +22
-3d = 6
/-3 /-3
d = -2
So we have found d. We can solve for c.
c - 3(-2) = 11
c + 6 = 11
-6 -6
c = 5
Now we know both D and C. d=-2 and c=5
