Both ‘Shall’ and ‘Will’ are modal verbs used to express future tense.
If you’ve ever had any doubts whether to use shall or will in the Simple Future Tense, WILL is used for all persons in both singular and plural.
We will begin to work in September.
How long do you think this heat will last?
The shops will be open at 8 o’clock tomorrow morning.
However, in more formal English, there is a rule which states that we should use SHALL in the first person only for phrases referring to offers and suggestions.
It’s so hot! Shall I open the window?
Shall we go? I’m tired.