If the triangles are similar, the proportion of the legs on the left to the legs on the right will be equal. This proportion would look like:

(You needed to combine the orange segment and the yellow segment to find the total length of the large triangle).
Now, cross multiply and solve for x:
28x+14=30x
*Subtract 28x from both sides to isolate the variable*
14=2x
*Divide both sides by 2*
7=x
Hope this helps!!