Valeria summoned birds to help her peel some beans. They began at $$7$$ o\textquotesingle clock, and as they became more and more skilled, they peeled $$20$$ beans from $$9$$ o\textquotesingle clock to $$10$$ o\textquotesingle clock, $$28$$ beans from $$10$$ o\textquotesingle clock to $$11$$ o\textquotesingle clock, and $$36$$ beans from $$11$$ o\textquotesingle clock to $$12$$ o\textquotesingle clock. During each hour, more beans were peeled than the previous hour, and the increments were the same. How many beans did Valeria\textquotesingle s birds peel in the first hour? 
Overseas Competition->Knowledge Point->Calculation Modules->Sequences and Number Tables->Arithmetic Sequences