We can see if the first two options are correct. The first one is eliminated because when x is 2, y is 5 and there is not a different of 5, only 3. This could make you think that the second option is the right answer, but when x is 1, y is 6 and the difference is 5, not 3.
The third choice we could try out.
6=-(1)+7
5=-(2)+7
4=-(3)+7
3=-(4)+7
Let's look at the graph also. The coordinates are on the line.
So the third option, y=-x+7
1) 2500
3) 450
5) 98.7
7) 4200
The answer should be 5. If your asking what number multiply's to the third power, then it's 5. 5x5x5= 125.