25-(y+3)=10

my notebook says the answer is 12 ... but

28-y = 10

-y = 10-28

-y . = -18

???

25 - (y+3 )= 10 apply the negative over the terms in the parentheses

25 - y - 3 = 10 combine like terms on the left side

22 - y = 10 add y to both sides, subtract 10 from both sides

12 = y