А)(42-32)*53-(42-32)*63=10*53-10*63=530-630=-100
б)79*(45+55)-89*(45-55)=79*100-890= 790-890=-100
в) (75-45)*88+12*(75-45)=30*88+12*30=30*(88+12)=30*100=3000
г) 392*(23+77)-492*(23+77)=392*100-492*100=(392-492)*100=-100*100=-10000
300-200=100кв м 1500:100=15кг-с одного метра 15*200=3000кг=3т 15*300=4500кг=4.5т
12,31,24,12,51,44,12,71,64,12,91,84
1/4:(-42/5)•(-7/6)= 1/4•(5/42)•(-7/6)=5/168•7/6=5/144