The difference in gallons per day used is 3.6.
The formula to calculate a z-score is:

,
where X is the value used to calculate the score, μ is the mean and σ is the standard deviation. We have the z-scores so we must work backward:

For both equations, we will cancel the 1.2 by multiplying both sides:

Now we will cancel 2.2 from both equations by adding it to both sides:
3.6+2.2=X-2.2+2.2 and 0+2.2=X-2.2+2.2
5.8=X and 2.2=X
The difference in gas used per day would be given by
5.8-2.2 = 3.6.
Answer: 15.3 miles
Step-by-step explanation:
From the question, we are informed that Martin would like to start training to run a marathon and that first week he runs a total of 15 miles.
We are further told that he would like to run 0.3 more miles each week than the week before. There, the number of miles that Martin will run the second week will be:
= 15 miles + 0.3 miles
= 15.3 miles
A. is your answer
Hope this helps! :)