6d - 11/2 = 2d - 13/2
move all numbers with variables to one side and all constants to the other
6d (-6d) - 11/2 (+13/2) = 2d (-6d) - 13/2 (+13/2)
-11/2 + 13/2 = 2d - 6d
2/2 = -4d
1 = -4d
isolate the d, divide -4 from both sides
1/-4 = -4d/-4
d = 1/-4, or -1/4
hope this helps