Răspuns:
fratele mai mare=F
fratele mai mic=f
F=fx5
F-6y=f-y
fx5-6y=f-y|+y
fx5-5y=f|-f
fx4-5y=0
fx4=5y|x5
fx20=25y
Fx4=25y
F-6y=f-y|x4
4F-24y=4f-4y
25y-24y=4f-4y
y=4f-4y y=280x4 y=1120lei
f-y=280lei
f-1120lei=280lei
f=1120lei+280lei
f=1400lei
F=fx5
F=1400leix5
F=7000lei