Hi ... If you draw a diagram, you'll see that triangle DAB and DCA are sort of "anti-similar", that is, when you list corresponding vertices, you'll be reading the vertices of one triangle clockwise and the other counter-clockwise. Your book or teacher has listed the vertices correctly ... D to D, A to C, B to A. you could probably get away without explaining or even understanding why this must be so, but if you can understand why, that will be helpful for you.

Now all you have to do is write out the proportions, remembering that corresponding sides of the similar triangles are in proportion. Plug in the values you know. Remember that, for example, AD=DA, CD=DC etc, doesn't matter the order (we're using absolute values here, not directed distances).

See the pdf.

I managed to make another pdf from GSP, showing the situation. When you construct a cevian so that there are two similar triangles, the similarity will always be opposite in the sense I explained. There's a word for it, though I can't remember it right now.