Excuse if I have this wrong but I’m going to guess that in every question how the 2 is up the m or the other letters that means you are multiplying that number/ letter by its self one more time so I’m not really sure, I’m sorry.
X=15
expand the brackets and collect like terms so 6x+15=7x
then -6x to get x=15
Answer:
As problem is of regression analysis,thus r^2 will be 24 and sy/x is 4.
The answer is 5.
You just plug whatever number is in the f(?) part in for x!