5×b+4×r=1000
r=b+70
5×b+4×(b+70)=1000
5×b+4×b+4×70=1000
9×b+280=1000
9×b=1000-280
9×b=720
b=720:9
b=80 ( pentru o bluza se folosesc 80 cm)
5×80+4×r=1000
400+4×r=1000
4×r=1000-400
4×r=600
r=600:4
r=150 (pentru o rochie se folosesc 150 cm)
verificare
5×80+4×150=400+600=1000 (Adevarat )