algebra
posted by John .
There is a slow leak in your bike tire. The average rate of change of air in your tire is 2 pounds per square inch per day. The amount of air in your tire is now 70 pounds per sqsquare inch. Find the amount of air that will be in your tire in 5 days

How about multiplying 2 pounds by 5 days? Then subtract your answer from 70.

find the sum of the first 22 terms of the arithmetic progression, if the firstr term is 3 and the common difference is 7.

70  2t, where t is the time in days (in this case, 5). That would give you an answer of 60 psi. (psi = Pounds per Square Inch)
A more accurate formula would take into account that the leak rate is proportional to tire pressure. They probably don't expect you to know that, since that involves physics.
The more accurate formula would be
70 *(68/70)^5 = 60.56 psi