Answer:
To set up this equation, we want to find the total change in time (x) over 4 years if every year your time decreases by 6 seconds. Our equation should look something like this:
x = 6*4
To solve this, you just have to multiply 6*4!
x = 24
This means that over 4 years, you have cut 24 seconds off of the time it takes you to run a mile! Your total change in time would then be 24 seconds!