At first, Felicia : Siti = 5 : 7. Let Felicia = 5u, Siti = 7u.

[[model:questions/solutions/q5403.png]]

• After transfer: Felicia = 5u + 15, Siti = 7u − 15
• Given answer: Felicia in the end = 30
• 5u + 15 = 30 → 5u = 15 → u = 3
• Felicia at first = 15, Siti at first = 21
• Siti in the end = 21 − 15 = 6
• Check: Siti : Felicia end = 6 : 30 = 1 : 5

Felicia had 30 pencils in the end.
Check: Total pencils = 15 + 21 = 36 = 30 + 6. ✓