Answer: One root
Step-by-step explanation:
x^3 = -343
x^3 + 343 = 0
x^3 + 7^3 = 0
(x+7)(x^2 - 7x + 7^2) = 0 .... sum of cubes factoring rule
(x+7)(x^2 - 7x + 49) = 0
Set each piece equal to zero and solve for x.
You should find that the first piece x+7 = 0 leads to x = -7 as the only real root.
The other piece x^2-7x+49 = 0 leads to two non-real roots, ie complex roots.