fie x suma de bani
dupa ce cheltuie 30% ramane cu x-30x/100=100x/100-230x/100=70x/100
din acest rest el cheltuie 4/ 7 adica 4/7 * 70/100=40/100
din suma initiala ii mai raman 70x/100-40x/100=30x/100
deci 30x/100=570
x=570:30/100=570*100/30 =570*10/3= 5700/3=1800lei
b) 1800+1800*15/100=1800+18*15=1800+270=2070lei
