notam:
p- prețul pixului
s- prețul stiloului
s-p=10
(s- 10% × s) - (p+20% × p)=6
100% × s-10% × s=90% × s
100% × p+20% × p=120% × p
90% × s - 120% × p =6
s-p=10
s=p+10
90% × (p+10) - 120% × p = 6
90% × p + 90% × 10 - 120% × p = 6
90% × p - 120% × p + 9 = 6
- 30% × p = - 3
30% × p = 3
30p = 300
p=10
s=p+10
s=20