Answer:
CD = 7
Explanation:
Given that the triangles are congruent, then corresponding sides are congruent, that is
CD = AB , substitute values
3y + 1 = 15 - 4y ( add 4y to both sides )
7y + 1 = 15 ( subtract 1 from both sides )
7y = 14 ( divide both sides by 7 )
y = 2
Thus
CD = 3y + 1 = 3(2) + 1 = 6 + 1 = 7