Hello I have an economics math equation and have provided the question via image. I need help with Suppose the marginal tax rate is 37 percent for an income level of $50,000 and 39 percent for an $80,000 income. This implies that the underlying tax structure is _____ in nature.

Suppose the marginal tax rate is 37 percent for an income level of $50,000 and 39 percent for an $80,000 income. This implies that the underlying tax structure is in nature. 0 a.lumpsum O b. regressive O c. xed 0 d.progressive 0 er proportional