poty a) 21-(32-25) = 21- 7 = 14

b) 44-(4x9-25)-12 = 44-(36-25)-12= 44 -11 - 12 = 21

c)61-(54-24:4) = 61 - (54 - 6) = 61 - 48 = 13

d)25- {20+[18-(13+10:2)]}= 
   25- {20+[18-(13+5)]} =
   25- {20+[18 - 18]} = 
   25- {20 + 0} =
   25- 20 = 5

e)69-[26+(67-42)] = 69- [26+25] = 69 - 51= 18

 f) 4+[(55-2x9)-(40:2+6)] = 
    4+[(55 - 18) - (20 + 6)] =
    4+[37 - 26] = 
    4+ 11 = 15