Add two files in linux

In linux, add the content of two files-general Linux technology-Linux programming and kernel information. For details, refer to the following section. A.txt
0 3
0 9
0 10
0 8
0 10
0 14
0 7
0 10
2 5
0 8

B .txt
1 80
1 68
0 118
24 187
1 120
68 213
5 125
197 223
7 141

Use SHELL to add the same fields of the two files: A. txt + B .txt:
1 83
1 77
1 127
......

The solution is as follows:
I,
Awk 'nr = FNR {a [NR] = $1; B [NR] = $2}
NR> FNR {print $1 + a [FNR], $2 + B [FNR]} 'a.txt B .txt

II,
While read-u3 a B & read-u4 c d; do
Echo $ (a + c) $ (B + d ))
Done 3 Newfile

III,
Awk '{print $1 + $3 "" $2 + $4}' <(paste file1 file2)