Hi didieravoaka,
Any time a Quant question includes a triangle, that triangle is almost always a part of how you have to answer the given question.
When dealing with criss-crossing lines, it's important to remember that opposite angles are EQUAL and the angles on one side of a line always add up to 180 degrees. Knowing those two rules...
1) In the upper 'right corner', we have 40/140/40/140
2) At the bottom, we have 130/50/130/50
3) We now know two angles in the triangle: 40 and 50, so the third angle in that triangle is 90. Since angles on one side of a line always add up to 180, we now know that X=90.
Final Answer: A
GMAT assassins aren't born, they're made,
Rich
