We have two similar triangles. One triangle has the lengths of 5 and 7, while the other has 2 and x. We can set these up as proportions.
Set the proportions by creating fractions with the corresponding side lengths.
It should look like this:
5/2 : 7/x
A quick way to solve for this is to find the scale factor- by dividing the numerator by it's denominator.
Divide 5 by 2.
5 / 2 = 2.5
2.5 is our scale factor, so we should divide 7 by 2.5 to solve for x.
Divide 7 by 2.5.
7 / 2.5 = 2.8
X = 2.8
Your answer is B.) 2.8
I hope this helps!