To predict a student's grade if they spend no time studying for the exam, we can substitute \( x = 0 \) into the trend line equation \( y = 5.03x + 56 \).
Substituting \( x = 0 \):
\[ y = 5.03(0) + 56 = 56 \]
So, if a student spends no time studying, we can predict their grade would be 56. Therefore, the correct response is:
56