Răspuns :
x=suma initiala
x+350+150-900=50
x+500-900=50
x+(-400)=50 / +400
x=450
x+350+150-900=50
x+500-900=50
x+(-400)=50 / +400
x=450
bani primiti 350+150=500
cheltuiti 900
rest 50
bani initiali 450lei(900-500+50=450)
cheltuiti 900
rest 50
bani initiali 450lei(900-500+50=450)