[Diagram is in the book, p. 177]
 

a.  Asks you to compute the values of various things:

Consumers' cost of the tariff:  This is the area between the old price line, the demand curve, the new price line, and the vertical axis, because that measures the difference between the value to consumers of what they bought at the old price, and what they buy at the new price (the area between the new price line, the demand curve, and the vertical axis, is part of the value to consumers of what they buy at both prices, so it washes out).  So we have the rectangle base new quantity (150) height the price difference (4000 - 3400 = 600) [i.e. 150 x 600 = 90,000] plus the triangle base quantity difference [200 - 150 = 50], height the price difference (600) [ i.e. area 1/2 base x height = 1/2 x 50 x 600 = 15,000].  So total value is 90,000 + 15,000 = 105,000.

Domestic producers' gain from tariff: This is the area bounded by the supply curve, the two price lines, and the vertical axis, so it is the rectangle (new quantity)x(price difference) [= 125 x 600 = 75,000] minus the triangle (new domestic production - old domestic production) [= 125 - 100 = 25] as base and price difference as height, [i.e.1/2 x 25 x 600 = 7,500].  So total is 75,000 - 7,500 = 67,500.

Tariff revenue = imports x tariff = (150 - 125) x (4,000 - 3,400) = 25 x  600 = 15,000.

Net social cost of the tariff = producers' gain + tariff revenue - consumers' cost = 67,500 + 15,000 - 105,000 = 82,500 - 105,000 = -22,500 [negative because it is a cost]

Note you could have gotten the social cost directly by adding the area of the two "deadweight loss" triangles that we added and subtracted above, i.e. 15,000 (part of consumers' cost) and 7,500 (which producers did not gain), also equals 22,500.

b.  Net social cost was 22,500, actually in dollars $22,500,000 because number of motorcycles is in thousands.  So cost per job if it saved 700 jobs is $22,500,000/700 = approximately $32,143.   But cost to consumers was higher, because they had to pay higher prices for all the motorcycles bought: the cost to  consumers was $105 million, or dividing by 700 $150,000 per job.

c. The quota with the same effect would have produced the same quantity of imports, i.e. 25,000.
 

>Problem 3 (part b: what will the qty of imports be?)
>
If they can be imported freely at $3,000 each, the US price will be $3,000 each (assuming identical domestic and imported product).  So at that price, the domestic supply is 700, domestic demand is 1,300; the difference will be imported, i.e. 600.