It is so very simple and quick to get the answer, especially since, if you need it, you can use the calculator that comes with your computer. But since you are obviously not able to do so, the answer is 690.
345 + 345 = 690
345 + 890 + 549 = 1784
2 + 345 = 347
200 + 345 = 545
345 + 67797808 = 67798153
325 + 345 = 670
345 + 253 = 598
345 + 890 = 1235
345 + 435 = 780
345656 + 345 = 346001
55555555 + 345 = 55555900
1 + 55 + 345 + 87 + 98 = 586
345 + 69 = 414