Possible Clues:

• Something that needs solving
• Shortly, exploratory spacecraft meets another in difficulty
• One hard to understand, solve
• Word after word, in math class
• Difficulty finds British and the French involved in concert
• A matter hard to solve
• It may require an answer, that's the difficulty
• Hurdle for batsman ends with the French
• Part of a math test
• Poser for child? This child sets a poser for teachers