a) 18/10•(23/9+27/9)=18/5•50/9=20
b) 15,44-(123-12)/90-13=244/100-111/90=61/25-111/90=1258/450-555/450=297/450=33/150=11/50
c)4,25-0,3•(416-41)/900=4,25-3/10•375/900=4,25-1/8=425/100-1/8=17/4-1/8=32/8-1/8=31/8
d) (223-22)/90-24/10-15+(12•6+5)/6= 201/90-12/5-15+77/6=67/30-12/5-15+77/6=67/30-72/30-450/30+385/30=70/30=7/3