Divide the image length M'P' over its corresponding preimage length MP
(length of M'P')/(length of MP) = 4/10 = 2/5 = 0.4
Answer: 0.4 which is choice C
The fact that the scale factor is less than 1 and its positive means that the image is smaller than the preimage (aka the figure shrinks). The result is positive because we don't have any reflections going on.