Differential piecework payment scheme – calculating wages

A differential piecework payment scheme operates in the packing department of a factory. Straight piece rate is $ 10 per unit. Details of the scheme are as follows:

Units packed per week ——- premium rate per unit

1-2000 units per week ——- 50 cents per unit

2001 to 3000 units per week ——- 65 cents per unit

3001 to 4000 units per week ——- 75 cents per unit

Only extra units packed, over the previous threshold, qualify for the higher rates.

If 3240 units were packed, how much would be paid in wages??

A. $15,274

B. $ 24, 876

C. $ 30,000

D. $ 34, 230

I get D by calculating premium rates for 3240 units and adding in the standard ($ 3240 * $ 10).

Is this solution correct??