Answer: x = 4
Explanation:
since it is showing us that the angles are congruent, we know that the smaller triangle is just a scaled-down version of the larger one. in other words, it is the EXACT SAME triangle, just slightly smaller.
so, i redrew them next to each other, so i could compare them easily.
i looked at the corresponding sides that were given, and realized that the side that is 10 on the larger triangle is equal to 5 on the smaller triangle. the side that is equal to 6 on the larger triangle is equal to 3 on the smaller triangle. this concludes that the smaller triangle is exactly half the size of the larger triangle!
so, i figured (using logic) that x must equal 4, simply dividing its corresponding side (with a measure of 8) in half.
hope this helps! xoxo