It will help you if you will redraw the triangles so they
are turned the same way, and so that their bottom sides are
at the same level.  They give them to you turned in different 
ways just to confuse you as to which sides correspond.

Redraw them like this so you can compare corresponding sides:



The vertical side KL of the first triangle corresponds to the vertical
side ST of the second triangle 

in the same way that

The horizontal side JL on the first triangle corresponds to the horizontal
side RT of the second triangle.

x compares to 10 just as 15 compares to 25.

      x is to 10 as 15 is to 25

"is to" is "over" and "as" is "equals".

   

Solve that by cross-multiplying then dividing.


Edwin