Decide which problems can be solved by using proportional reasoning. select all that apply

a: yani buys 4 dozen flyers for $7.25.what is the cost of 12 dozen?

b: first-class letters cost $0.49 for the first ounce and $0.22 for each additional ounce. what is the cost of a 5-oz letter?

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.