Well, 15% of 60 is 9 so now you have to create a model :)
3x8+4 because 3 times so that is 3 x the sum of 8 and 4 so 8+4 together it would be 3x8+4
If the order of the numbers in the question are the order Darrin put theem in then no, his work is not correct. this is because 7.25 is not greater than 7.52. the real order should be 7.52,7.25, 5.72, 5.27
The answer is 3 because z to the y a-1