2. The cost of potatoes is proportional to the weight (in pounds) you buy. If potatoes cost $0.69 per pound, what is the cost for 3 pounds of potatoes? y=mx+b 3. Suppose that y is directly proportional to x. When x = 16, then y = 4. Let k be the proportionality constant. a. What is?m b. If x 32, what is y? c. If y 32, what is x? 4. Identify the slope and intercept in each of the following. When appropriate, state the units. a. y = 2.5x+6 b. y=-5x+20 c. She earns $9.25 per hour. d. To rent a car for one day, the cost is $25 plus $0.15 per mile. e. My new phone costs $25, plus a monthly charge of $15.