Answer:
My uncle is 78 years old. 
Explanation:
Let the age of your uncle be x. 
400 - 2x = 244
Shift (-2x) to the other side and change it to (+2x). 
400 = 244 + 2x
Shift (+244) to the other side and change it to (-244). 
400 - 244 = 2x 
Evaluate. 
2x = 156
Find x. 
x = 156 ÷ 2
x = 78