He demonstrated the mathematical equation by solving it on the board.
Answer: 3
Explanation: The first letter in each word of a title is usually capitalized.
30
A little tricky. I think it is the best answer, but many people do not like participial phrases at the beginning of a sentence. This one seems fine. You might get nailed for being redundant. All quadrapeds have 4 feet. But there's nothing better.
31
I agree with your choice.
