Why dose a triangle form 180 degress

Graham’s monthly bank statement showed the following deposits and withdrawals. -$25.20, $42.75, -$22.04, -$18.50, $74.11. part a if grahams baldness in the account was $37.86 at the beginning of the month,! 27/4! 2// the account balance at the end of the month? ? plz i will give you 100 points