A subordinate idea in the sentence is the part of the sentence that does not convey a complete idea or thought and needs the main sentence to complete its message. The subordinate idea in the given sentence above is "After we found the classroom". This is introduced by the subordinating conjunction "after".
They can tell you what you need to fix,work on,etc.
I think the answer is YEWS but I'm not 100% sure. Hope this helps!!!!