The two lines of longitude that are found opposite from one another will always add up to?

360°

Explanation;

Lines of longitude are imaginary lines that used along with latitudes allow us to be able to locate points on Earth. Longitudes are drawn vertically on maps with the most popular one being the Prime( Greenwich) meridian.

As the Earth is spherical, the lines of longitude encircle the Earth which means that an entire longitudinal line will be 360°. As maps are flattened out, the longitudinal line is divided into 2 such that the longitudinal lines seen on a map are 180° each. When a line of longitude is added to its opposite, they will reform the original line that runs around the earth thereby making 360°.