Verified answer

(x + 21) - 10 = 20

x + 11 = 20

x = 9

20=(x+21)-10

(20+10)-21=x

X = (20+10)-21

(x + 21) - 10 = 20

(x+ 21) - 10 = 20

(21+x)-10=20

the bracket are not necessary btw