Is the number of hours spent studying an explanatory variable

Yes because it is the amount you are studying.

Yes, because it's a type of amount.

The answer would be b

38+105= 143, 39+104=143, and you will find then adding the numbers on opposite sides, moving inwards yields the answer 138 every time. because of this, you’re going to multiply 138 times the number of pairs, which is 34. therefore, 34*138= 4692(i’m sorry if it’s the wrong numbers, but it’s the right concept)