Answer:
If two pairs of corresponding sides are in proportion, and the included angle of each pair is equal, then the two triangles they form are similar.
Compare their two sides,
8 and 2, 8=2×4
12 and 3, 12=3×4
the two corresponding sides are in proportion,
And based on observation, we can basically assume that the corresponding angles have the same degree,
thus, these two triangles are similar triangles.
so x should also be the 4 times of 3,
x=3×4=12