Given:
Four lines are marked proportion, the length of TW can be determined by

Value of a:
Let us set the proportion for the given lines.
Thus, we have;



Thus, the value of a is 5.6
Value of b:
Let us set the proportion for the given lines.
Thus, we have;



Thus, the value of b is 5.
Length of TW:
The length of TW is given by


Thus, the length of TW is 13.6