Answer:
d = 2A/b - 4
Explanation:
"Solve for d" means, "get d by itself."
What are all the things acting on d? The division by 2, the multiplication by b, and the addition of 2b. So we need to "undo" all those things.
First you take care of anything added or subtracted, so subtract 2b from both sides:
A - 2b = 1/2(bd)
Did you follow that? It's pretty standard.
Now get rid of the 1/2 by multiplying each side by 2:
2(A - 2b) = bd --> 2A - 4b = bd
Good? Now "undo" the b multiplier by dividing both sides by b:
(2A -4b)/b = d
Then just turn it around:
d = (2A - 4b)/b
You could do the "divide by b" in the right side to get:
d = 2A/b - 4
Either form is equivalent, just whichever you think they'd want.