Answer: (4x+12) - (2x-5)
Step-by-step explanation: The (4x+12) is positive and the (2x-5) is negative.
Answer with positive exponent =
or 
Answer with negative exponent = 
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Explanation:
The rule we use is

If we multiply two exponential expressions with the same base, then we add the exponents.
The base for each is 5. The exponents 4 and -7 add to -3.
This means

To convert to a positive exponent, we apply the reciprocal to the base. We go from 5, aka 5/1, to 1/5.
So, 
A. At the very end
B.one more away from that
C.on the left
A) 3b-7b
-4b
b) a+a-5a
-3a
c) -3-3r
cannot be simplified, no like terms
d) 7t-8t-8
-t-8
e) -15p-20
cannot be simplified, no like terms
f) -g-g-g
-3g