>>1.subtract (10a^{2}-4) from (a^{2}-7a-9)
In this case, you need to combine like terms: 10a^{2} and a^{2} are the same term so you subtract them. The same goes to the other term
>>2.simplify. answer w/ positive exponents.
-21a^-2bc^5 -3a-bc^5
------------ = ------------
14a^-6bc^-2 2a-3b(1/c^2)