Blossom's Flowers Purchases Roses for Sale for Valentine's Day

Blossom's Flowers purchases roses for sale for Valentine's Day. The roses are purchased for $10 a dozen and are sold for $20 a dozen. Any roses not sold on Valentine's Day can be sold for $5 per dozen. The owner will purchase 1 of 3 amounts of roses for Valentine's Day: 100, 200, or 400 dozen roses. If the probability of selling 100 dozen roses is 0.2 and 200 dozen roses is 0.5, what is the probability of selling 400 dozen roses?

A) 0.5
B) 0.2
C) 0.7
D) 0.3