Ok what you have to do here is replace the variable t in each equation with the values given by the table. Doing this you'll be able to calculate every value for d. If those values are the same as the ones showed in the table then that's the right answer.
Let's try with equation A:
For t=20:
For t=40:
For t=60:
And for t=30:
So our d values are 2, 4, 6 and 3 and they corresponds to t values 20, 40, 60 and 30. Our values matched with those of the table, therefore the equation in item A is the correct answer.