You would round 313 to 300 and 489 to 500 and multiply 300 by 500. You should get 150,000. The real answer should be near 150,000.
The product of 20 and 35 is 700.
489 squared is 239,121.
35 is the product of 10 and 3.5. If you mean integers though, 10 is not a factor of 35.
35 multiplied by 20 is 700.
35 multiplied by 12 is 420.
4 x 35 = 140
35 multiplied by 87 is 3,045.
375 + 489 = 864
1, 3, 163, 489
489 - 2 = 487
1, 3, 163, 489