I believe the answer is the second one
3x - 8 = 2x + 15
Add 8 to both sides
3x = 2x + 23
Subtract 2x from both sides
x = 23
I’m not sure about the estimates but the overall answers should be correct
No, there is no 'greatest integer'. That is because positive numbers can go up tp infinite, and we do not know where numbers stop.
However, there is a negative greatest integer because the ones that's closes to zero is -1.