Direct proportional equations are always in the form y = kx, where k is some constant. In the case of choice B, we have k = 1/4. Visually, direct proportion equations are always straight lines and go through the origin.
Divide $34.99 over 9 to get 34.99/9 = 3.88777 approximately. This rounds to 3.89, so it costs $3.89 per pound. That's the unit rate. Multiply this by 6 to get 6*3.89 = 23.34 which is the cost of the 6 pound turkey.