Narada Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · Signs, Planets, Birth
जातकम् १
त्रिकोणस्थस्य चाष्टाक्षिसूर्या द्यूनगतस्य च ।तुर्याष्टगस्य तु स्वर्गा गुणकाः परिकीर्तिताः ॥ १४० ॥
In the full Narada Purana (Purva Bhaga) this is chapter 55, verse 140.
For one in a trikona (luck house), 28. For one in the 7th, 12. For one in the 4th or 8th, 21. These are the multipliers.
Simple meaning: Planets in the luck houses, the 7th, and the 4th or 8th get their own shares.
षड्वर्गार्द्धस्य त्रिंशस्य त्रिकोणगश्च स्मरगः ।
Planets share the sub-periods by their house from the period lord.
क्रमः केंद्रादिकोऽत्रापि द्वित्र्यादौ सबलस्य च ।
The period lord's share is 84, a planet with it 42.
दशागुणैर्हता भक्त्या गुणैक्येन समागताः ।
Periods are multiplied by their multipliers and divided to give years and months.