Answer:

Explanation:
Step 1: Write out equation
d(-3 + x) = kx + 9
Step 2: Distribute d
-3d + dx = kx + 9
Step 3: Subtract 9 on both sides
-3d + dx - 9 = kx
Step 4: Subtract dx on both sides
-3d - 9 = kx - dx
Step 5: Factor out x
-3d - 9 = x(k - d)
Step 6: Divide both sides by k - d
