So,
We can "translate" this sentence into mathematical form.
"A number"
n
"increased by negative four"
-4 or + (-4)
"is equal to seventeen."
= 17
So it can be either n - 4 = 17 or n + (-4) = 17. It can also by -4 + n = 17, etc.
Clearly, option B is the only one that qualifies as an accurate "translation" of our sentence.