After Sally had given 1/9 of her stamps to Andy, she had 280 stamps (since they now have equal shares). So 280 was 8/9 of what she started with, making the 1/9 she handed over equal to 280/8, that’s 35. And Andy was “under” by the same amount she was “over” an equal share, that’s 35 under matching her 35 over, which is 70 altogether.
By all means use algebra but you may find you can reason a word problem through in words.
It is saying that the Balance was 21 if he wrote a check for 30 and The bank was charging him $35 for overdrawing his account of basically you’re gonna just Add so 21+30+35 is 86