Question

How many seconds are there in a year ?

Answer 1

This is just a series of conversion factors.
$$1\ year = \dfrac{365\ days}{1\ Year} \times \dfrac{24\ hrs}{1\ day} \times \dfrac{60\ min}{1\ hr} \times \dfrac{60\ sec}{1\ min} $$
You can see the all terms cancel seconds (numerator) and year (denominator)
Plugging into a calculator, $$365 \times 24 \times 60 \times 60 = 31,536,000$$
So the answer is that there are $$31,536,000$$ seconds in a year.