Answer: Calculus.
Step-by-step explanation: He created calculus.
I believe A and B are the ones. As for explaining? hmm. I would honestly say that any number to the right of a number is a tenth of the place above it. But then again, it's optional to explain ;P
The given equation is

And we have to solve for y.
Solving for y, means isolating y . And to isolate y, we need to get rid of 4 that is with y .
It means we have to separate 4 from y, and for separation , we have to perform division. That is, we have to divide both sides by 4, and that will be the next step .
So out of the four options, correct option is the last option .