Which continent once joined Greenland?

Correct answer is North America, which were a part of the so-called continent Laurasia. It was a continental mass, that included Asia, Europe, Greenland and North America.

Explanation:

According to geologists this supercontinent existed until between 66 and 30 million years ago. According to them actually there were continents, one in northern hemisphere, called Laurasia and the one in the southern hemisphere - Gondwana.

the answer would be the third option, "no, ariel should have added 9^2 and 12^2 and compared that to 15^2."

this is found through the pythagorean theorem, which is a^2 + b^2 = c^2.

this is the correct way of solving the problem:

9^2 + 12^2 = 15^2

81 + 144 = 225

225 = 225