Ajutor la ex 16 repede!Dau coroana!!!

Răspuns:
a) (30+40)+(45-15)
70+30=100
b) 4×5+20
20+20=40
c) (36-21)+(20-12)
15+8=23
d) (24+16)-(18-9)
40-9=31
c)