Sum for column from multiple tables ms sql

Question

Select

 

Table 1
id Item quantity
1   a       2
2   b       6
3   a        3



Table 2
id Item quantity
1   a       1
2   b       16
3   b       3


Table 3
id Item quantity
1   a       2
2   b       6
3   a        3


Table 4 reslut need to be
id Item quantity (sum from other tables)
1   a      11
2   b       31