Being the eldest son of king Dasaratha and widely known as Rama you happen to be the heir apparent. Hence, Oh ! king, accept the kingdom and look after the people. [2-110-34]
इक्ष्वाकूणां हि सर्वेषां राजा भवति पूर्वजः | पूर्वजे नापरः पुत्रो ज्येष्ठो राज्येऽभिषिच्यते || २-११०-३५
In the line of the Ikshvakus, only the eldest son becomes king. When the eldest is living, a youger son cannot become the king. The eldest son alone is consecrated in the kingdom. [2-110-35]