Answer:
5/2
Step-by-step explanation:
Start by eliminating parentheses.
... 2n +4 +6 = -9 +8n +4
... 10 = -5 +6n . . . . subtract 2n
... 15 = 6n . . . . . . . add 5
... 15/6 = n = 5/2
_____
Check
(2·5/2 +4) +6 = -9 +4(2·5/2 +1)
5 +4 +6 = -9 +4(5 +1)
15 = -9 +24 . . . . . true, so the answer checks OK
