Answer:
[tex]\frac{3}{6} =\frac{7}{6+x}[/tex]
Step-by-step explanation:
There are two similar triangles in this figure. The small one has a base of 6 and a height of 3.
The bigger triangle has the smaller one included in it, so you must add together the bases, 6 and x, and the heights, 3 and 4, to get the proportion.