Answer: -13
Step-by-step explanation: When you have two numbers with negative signs, you add them but you keep the negative sign.
Therefore, -6-7 = -13
For the future, know these rules for signs when adding, subtracting, dividing and multiplying:
When adding two negative numbers, you add but keep the negative sign like in the above problem.
When adding a positive and negative, you subtract but keep the sign of the highest number. Example: -4+9 = 5 or -11+3 = -8.
When multiplying two negatives or positives numbers, the answer will be positive. When multiplying negatives x positive = negative.
The same applies to division. (-)/(+) = (-) or (+)/(-) = (-)
(-)/(-) = (+)
Hope this explanation and rules help.