(a) Arrange the numbers in the decreasing order;

837+363+208

Now make pairs,

= (837+363) + 208

= 1200+208

= 1408

(b) Arrange the numbers in decreasing order,

= 1962+1538+647+453

Now make pairs,

= (1962+1538) + (647+453)

= 3500 + 1100

= 4600