A way to find the median of a set of numbers is by listing each number one by one and then slowly crossing out the smallest and biggest number one by one. If you end up with two numbers left, then you take the mean of those numbers. To do that, you add the two numbers and divide it by two.
If triangles are similar, that means their angles are equal and sides are proportional.
If you already have a proportion of two corresponding sides between triangles, then use that proportion and set it equal to a side you already know the measurement to. Hopefully that side is corresponding to your missing measurement, and you can then solve it.
