Answer:
x = 28
Step-by-step explanation:
Given a line parallel to a side of a triangle and intersecting the other 2 sides, then it divides the sides proportionally, that is
[tex]\frac{AC}{CR}[/tex] = [tex]\frac{AD}{DR}[/tex] , substitute values
[tex]\frac{10}{x}[/tex] = [tex]\frac{15}{42}[/tex] ( cross- multiply )
15x = 420 ( divide both sides by 15 )
x = 28
