Answer:
The slope is

Step-by-step explanation:

Their error is that they divided 12 by 30, instead of 30 by 12 in order to get the price per pair
the correct unit price is $2.50 per pair
2.5 * 12 = 30
Answer:
Don't subtract exactly or it will be incorrect, you'll have to add the years, and differentiate the leap years
Step-by-step explanation:
30 yrs old
sorry I dont have a shorter method