Answer:
As hard as this may seem, it's actually quite simple. Because these two figures are similar, their sides can be compared.
See how on the left side of both of the triangles the numbers are 4 and 8? This shows that the left triangle is twice as small as the right one, which means that if you multiply any of the sides of the triangle on the left by 2, you'll get the triangle on the right.
We can apply this to w. Look at the left triangle on the bottom and see how there is a 3. Well, we've already noticed how the triangle on the left just needs to be multiplied by 2 in order to get to the one on the right, so that's what we should do! When you multiply 3 by 2, you get 6 which is w.
So, long answer short, w is 6.