Answer:
d = -4
Step-by-step explanation:
3d – 4 + d = 8d – (-12)
3d - 4 + d = 8d + 12
4d - 4 = 8d + 12
(4d - 4d) - 4 = (8d - 4d) + 12
-4 = 4d + 12
-4 - 12 = 4d (+ 12 - 12)
-16 = 4d
-16/4 = 4d/4
d = -4
Okay, let's find out how much the tax was by finding out what 7% of $28 is, we do this by multiplying:

Convert 7% into a decimal, we do this by dividing it by 100 because percentages are parts of 100:

Multiply:

So this is the tax. Add it to the original price to get the total price:
Domain: What are all the possible x values?
[-6, 0) U (0,2)
[ ] Closed brackets means including a number
( ) Open brackets means not including that number
Range: All possible y values
(1, 6]
85% is 0.85 decimals
85 percent of 30
30 * 0.85 = 25.50
30-25.50 = 4.50
Solution: after sale, it is $4.50