If we want to make quadrilateral TUVW a parallelogram, we need to set the next equality SU= SW.
This is given because diagonals on a parallelogram bisect each other.
Now, we need to replace:
SU= SW.
b + 18 = 4b
Solve for b:
18 = 4b - b
18 = 3b
6 =b
Hence, the correct answer is b=6.
