Find the sum 5,-7
a. 2
b. -2
c. -35
d. 12

5-7 is your question. 
When you have a negative and a positive number and you are adding them, the negative number is going to be diminished by how many positive numbers you have. If we find the absolute value of both numbers and then subtract them we will get a smaller number. 
The absolute value of -7 is 7.
The absolute value of 5 is 5. 
So now we will subtract 5 from 7 and we get 2. 
To find out if it is negative or positive we look at the absolute values of our original numbers. 
Which one is greater? 7 or 5? 
7 is the greater number. 
7 was originally a negative. 
Since this had the greatest absolute value we use this numbers original sign. Which is negative. 
So your final answer is B. -2.