So if they have two angles in common, then all three angles must be in common. So they are similar triangles, which means the ratio between corresponding sides must be the same. So we know that the ratio of x to y must be the ratio of this entire base, which is x plus 10, to the height of the larger triangle, 220. And right there, we have a relationship between x and y. And if we take the derivative of both sides with respect to t, we're probably doing pretty well. Now, before taking the derivative with respect to t, I could do it right over here just to simplify things a little bit. Let me just cross multiply.