Answer: 
$78,000 
Explanation: 
The computation of interest at year end is shown below:- 
Interest at year end = Cash contribution + Income of partnership + Share of partnership liabilities - Cash from the partnership 
= $50,000 + $20,000 × 50% + $60,000 × 50% - $12,000 
= $90,000 + $10,000 + $30,000 - $12,000
= $78,000 
Therefore for computing the partnership interest at year end we simply applied the above formula by considering all the items given in the question