Answer:
The sum of 78 and a number is 105.
Explanation:
"The sum of 78 and a number is 105." will best describe "105 = 78 + y".
What makes the other answers wrong:
"The number 105 is more than 78." would be 105 > 78.
"The sum of 105 and 78 is a number." is 105 + 78 = y.
"Seventy-eight is more than the number one hundred five." is not true.
78 is less than the number 105.
Brainilest Appreciated.