A line segment of length $21$ has $d.r.=(2,-3,6)$ and makes obtuse angle with $x\:axis$, then the components of the line segment (vector) are?

Question

$(a)\:\:(6,-9,18)\:\:\:\qquad\:(b)\:\:(2,-3,6)\:\:\:\qquad\:(c)\:\:(-18,27,-64)\:\:\:\qquad\:(d)\:\:(-6,9,-18).$