akingba wrote:

From your solution, it's obvious we assumed the lines are all equal. As nothing in the question suggests that.

Hey there, akingba, we don't actually have to assume that the lines are equal. We only assume that opposite pairs of angles are equal. Whenever two lines cross, they will create two pairs of opposite angles, and these opposite angles are equal. For instance, s and v form one pair of opposite angles. Hence, s = v, no matter the length of the lines.