Find first letter from a list

[DariusCG]

Hello. I have function that finds first letter in all words from list. And I want to count all lower cases. I don't understand why quantity updates only once.
arr=[["Hello","how","are","you"],["I","am","fine"]

def first_letter(x):
    abc = "abcdefghijklmnopqrstuvwxyz"
    quantity=0
    for j in range(0,len(x)):
        letter= x[j][1]
        if x[j][1] in abc:
            quantity=+1
            
            
    print(quantity)