Answer:
x = 28
Step-by-step explanation:
If a line parallel to one side of a triangle intersects the other two sides of the triangle, then the line divides these two sides proportionally.
Then x/(x +10) = 42/(42 +15)
x(57) = 42(x + 10)
57x = 42x + 420
15x = 420
x = 28
