We can tell that the whole L shaped angle is 90 degrees because it has the little box in the corner. Now, the 90 degree angle is split into two parts with that line coming from the box. Those two parts of the whole 90 degree angle add up to 90 degrees.
90 = 4v + 2 + 9v - 3
Now, let's solve for v. Combine like terms.
90 = 13v - 1
Add 1 to both sides.
91 = 13v
Divide both sides by 13
7 = v
