I need more help with this mathe problem i dont get it

Umm.. just started this 2day and its not on my notes(p′︵‵。)

Rearrange the formula c^2 = a^2 + b^2 for b

Last year, a state university received 3,560 applications from boys. of those applications, 35 percent were from boys who lived in other states. part a)how many applications did the university receive from boys who lived in other states? part b)applications to the university from boys represented 40percent of all applications. how many applications did the university receive in all? i don't how to do part b so me and plz tell how you got your answer