Let us draw a triangle ABC with A=15° ,B=113° and b=7.
Please see the attached image.
We know that the sum of interior angles of a triangle is 180 degrees. Thus, we have

Apply Sine rule in the triangle ABC, we get

Therefore, we have

Answer:
Step-by-step explanation:
Tan(51) = opposite / adjacent
The adjacent side makes up the reference angle (51o)
The opposite side is not part of the reference angle
adjacent side = x
opposite side = 16
Tan(51) = 16 / x Multiply both sides by x
x * Tan(51) = 16 Divide by tan 51
x = 16 / tan(51)
tan(51) = 1.2349
x = 16 / 1.2349
x = 12.96
I believe it would be the third option