Explanation:
ABC and ADE are similar triangles.
that means they have the same angles, and all side lengths of one triangle correlate to the side lengths of the corresponding sides in the other triangle with the same factor.
so, know the factor of one pair of corresponding sides, you know the factor for the other sides too.
therefore, ED (x) relates to BC (2) with the same factor, as AD (4+3) to AB (4).
x/2 = (4+3)/4 = 7/4
x = 2×7/4 = 7/2