Answer:
y = 21
Explanation:
According to the Side Splitter Theorem, if a line parallel to one side of a triangle intersects the other two sides, then this line divides those two sides proportionally.
Therefore, according to the Side Splitter Theorem:

From inspection of the given triangle, the lengths of the line segments are:
To find the value of y, substitute the given line segment lengths into the proportion and solve for y:

Therefore, the value of y is 21.