Answer:
n = 7
Step-by-step explanation:
Let n represent the number. Then 3n = -n + 28, or 4n = 28.
Dividing both sides by 4 yields n = 7.
Check: "3 times a number" is 3n = 21
The "opposite" of the number is -7.
If we add 28 to this "opposite," we get 21. This is correct: 21 = 21
