The Diagram Below Shows Supply and Demand Diagrams (S and D)

The diagram below shows supply and demand diagrams (S and D) for some product. The government then imposes an excise tax. The new supply curve is ST. FIGURE 18- 4
-Refer to Figure 18- 4. What is the value of the tax imposed on this product, in dollars per unit?

A) $3
B) $1
C) $2
D) $5
E) $4