Set up a proportional fraction relating RSV and RTU. Before doing that, sort out what RT is equal to;
Now, we can equate SR/SV with RT/TU. This is something we can do because they are similar, and therefore should have equal ratios between sides.
Cross multiply them, and solve for x.
That being said, the little cutout at the top left claims the answer is 8. If you verify my answer, it works out.