Answer:
-7 yards
Explanation:
Might help to line everything up
First play: gained 8 yards (+8)
Second play: lost 6 yards (-6)
Third play: gained 3 yards (+3)
Fourth play: lost 12 yards (-12)
Then put it all together and solve (I'll solve left to right):
(8-6)+3-12
(2+3)-12
5-12
-7
The final change in yardage was -7 yards