Answer : B! As you can see, you can go to the x axis, and go to number 4. Then go down to -2, and you will end up in point B!
To find the length of the base, we have to understand that area of triangle:
Base x height/2
Therefore we would multiply the area by 2 and divide by 4 to find the answer:
24x2/4
=48/4
=12
Therefore the answer is 12m.
Hope it helps!