So the area of a triangle is the following:
A =( B x H) / 2
Let's plug in what we've been told in the question
24 = (3B x B) / 2
48 = 3B x B
48 = 3B^2
16 = B^2
+ or - 4 = B
I would go with option C because if you plug in 4 in or -4 for B into the area of a triangle equation, you end up with + 24 in^2.