The sum of seven and a number is ten

3

Step-by-step explanation:

If we change this into an equation, it becomes:

7+x=10

If we move 7 to the other side and change the symbol, it becomes:

x=10-7

x=3

from the sentence, "tomorrow morning, akiko will arrive an hour late" depicts a third person perspective because it doesn't use any pronoun to replace akiko, the subject of the sentence, and it is in singular form since akiko is only one person.