(-2) - (-7) = 5
Think of it as you having a 2$ debt, then you get rid of a 7$ debt. Sorry for bad english, btw why don't you just use the calculator for that problem?
To add on to Cavallin ^^^
Theres also this thing called the double negative rule where if you have
(-2) - (-7) If you take away the parenthesis you see two negative symbols right next to each other
If ever you see that -2 - -7 the double negative turns into a positive so your new problem would be
-2 +7 = 5