George was riding his bike by some construction, and apparently got a nail in his tire. 5 days later he realized that the tire was losing air, and at that time it had a pressure of 52 pounds per square inch (PSI); he didn t have time to x it then, and then 8 days after getting the nail the pressure was down to 46 PSI. (a) Write a linear equation giving the tire pressure (P) in pounds per square inch in terms of the number d of days since he got the nail in his tire.​