I can't see what image the answer choices are referring to, so I can't answer the second half of your question, but let's start with the first part.
Y is already on the left, but to make it into a function form to enter into a calculator, you want y alone on the left side. The first step to getting a variable alone is to move away anything that is added or subtracted to it.
Looking at this equation, 5 is the only thing that is added to y.
5 - y = - Ix-7I
Let's subtract 5 from both sides, so y can be alone. The reason this works is that if you start with 5 and take away 5, you'll have nothing, which is just what we want on the left side. But this is an equation, meaning both sides have to be equal. So you have to do the same thing on both sides. That's why we subtract 5 from both sides.
-y = - Ix-7I - 5
We're almost there, but we have -y instead of y. So now, we need to divide by -1. Right now, y is multiplied by -1--that is why it says -y. So, we now divide by -1, because that undoes the multiplication. Again, because it's an equation, we have to divide every single term by -1, not just y. Because all 3 terms are negative, when we divide each one by -1, they all become positive.
So we are left with:
y = Ix-7I +5
