Serial numbers for a product are to be made using four letters followed by three digits. The letters are to be taken from the first nine letters of the alphabet with no repeats. The digits are taken from the 10 digits zero through nine with no repeats. How many serial numbers can be generated? I can't remember the exact formula to set this up.

if a1=-7 and an=an-1+6 write the explicit formula

John Mark is 38 years younger than Alondra. 9 years ago, Alondra's age was 3 times John Mark's age. How old John Mark now?

Betty's athletic trainer told her to follow the beginning exercise training schedule on day 1. On day 2, she is to increase all distances and times by that 1 4 of day 1. On day 3, she is to increase all distances and 1 times by that of day 2. What will be her training schedule on day 3? On day 1, each athlete will begin the morning as follows: 1 Jog.......2 mi 1-min 1 Walk.....1mi 2nd Walk.…..1 mi Rest....1

A bicycle wheel rotates 400 times per minute. If the rider removes his feet from the pedals, the wheel will start to slow down. Each minute, it will rotate only as many times as in the preceding minute. How many 4 times will the wheel rotate in the eighth minute after the rider's feet are removed from the pedals? The wheel will rotate about times in the eighth minute. (Round to the nearest integer as needed.)