The scale factor is -2. The answer is choice A
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How did I get this answer? By picking any pair of preimage and corresponding image points. Let's pick on preimage point A and its paired image value A'.
Note how the x coordinate jumps from -11 to +22. So we multiplied by -2 to do this jump. We can see that 22/(-11) = -2 is another way to get this. Similarly, the same happens to the y coordinates as well: -14/7 = -2.
In short, you multiply the preimage coordinate by the scale factor -2 to get the corresponding image coordinates. Points B and C will follow the same pattern.