Answer:
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
