Answer
a. $x=\pm 62.2 units $
b. The unknown vector is (-142.2, 65).
Work Step by Step
a. Use the Pythagorean theorem to find the 2 possible x components.
$$(x)^{2}+(-65)^{2} =(90)^{2}$$
$$x=\pm 62.2 units $$
b. Sum the vectors, with the second vector to be determined.
(62.2, -65) + (Vx, Vy) = (-80, 0)
The unknown vector is (-142.2, 65).
