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
We know that there are total 18 socks, and 3 blue pair P(picking pairs of blue sock)= 3/18 or 1/6 As a result, the probability that he will pick a pair of blue socks is 1/6. Hope it help!