In triangle XYZ, an exterior angle to angle X had measure 100° and an exterior angle to angle Z has measure 120°. Which side of triangle XYZ is the longest?

Side YZ is the longest

Step-by-step explanation:

The longest side is across from the largest angle.

Angle X must be 80° because its exterior angle is 100° and they're supplementary. Angle Z is 60° for the same reason. Inside a triangle is always 180°, and since the measures of angle Z and X add up to 140°, so there's 40° left, meaning angle X is the largest.

Angle X is across from size YZ, so that's the longest