If two vectors are not perpendicular to each other, how should you add them?

Resolve each vector into its x and y components.

First you have to determine the angle of the vectors. Based on this angle, you separate the horizontal and vertical components using the trigonometric functions sine and cosine. The horizontal component is solved independently from the vertical, and finally using the Pythagorean Theorem, you solve the combined answer of the vertical and horizontal components to reach your final answer.