6. (6-d)^2

1. Expand the expression: (6-d)(6-d)

2. Apply the distributive property (FOIL): 6*6 + 6*(-d) + (-d)*6 + (-d)*(-d)

3. Simplify: 36 - 6d - 6d + d^2 = d^2 - 12d + 36