If we are looking to simplify two trinomials, it is easiest to put them on top of each other and subtract.
7x² - 2x + 5 7x² - 2x + 5
- (3x² + 4x + 10) -3x² - 4x - 10
4x² - 6x - 5
Every number will have only 3 digits. In the ones place, there are 5 choices. For every choice of digit made in the ones place, there are 8 possible choices for the hundreds place (you can choose from 1-9, omitting whatever is used in the ones place), and there are 8 possible choices for the tens place (you can choose from 0-9, omitting whatever has already been used elsewhere).
So there are

such numbers.
What is your question ? for help !
Symmetric property i think but i’m not sure