Answer: C) 10
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Step-by-step explanation:
Reflect point B over line L, and you'll arrive at the red point B' as shown in the diagram below.
Notice that B and B' are the same distance from line L. Both are 1 unit away.
Now reflect B' over line M to get to point B'', which is shown in blue. Both B' and B'' are 4 units away from line M.
All three points B, B' and B'' are on the same vertical line.
Once we plot B'', count the number of spaces from B to B'' and you should count out 10 spaces total.