Before we solve, let's define what a scale factor is. A scale factor is a certain number that can be multiplied or divided by to get a smaller or bigger image that's similar to the current image.
We have 48 by 36 as our original.
It has been reduced to an 8 by 6.
This means we must divide.
Before we get into any complicated ideas, if any, let's try a simple trick.
Divide 48 by 8 and 36 by 6. This should give us a scale factor if they give us the same quotients.
48 / 8 = 6
36 / 6 = 6
It turns out our scale factor is 1/6 (the same as dividing by 6).
The answer cannot be 1/8 because 36 / 8 doesn't give us 8 as a quotient.
The answer also cannot be 6 because we'd have to mutliply our current sides by 6 to get the new image, which it was the opposite.
By elimination and work shown, A.) 1/6 is the correct answer.
I hope this helps!