If you would like to know the values of these numbers, you can calculate this using the following steps:
a + b = 1855
a - b = 259 ... a = 259 + b
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a + b = 1855
(259 + b) + b = 1855
259 + 2 * b = 1855
2 * b = 1855 - 259
2 * b = 1596 /2
b = 1596 / 2
b = 798
a = 259 + b = 259 + 798 = 1057
Result: The numbers are 798 and 1057.