This is poorly written, but as i understand:
We have the general equation:
y = x + i
where i is a constant, and we want this function to pass through the point x = 2 and y = 3.
Then we must find the value of y, we know that when x= 2 we also must have y = 3, so we can replace those two values in the equation above and get
y = 3 = x + i = 2 + i
3 = 2 + i
3 - 2 = i
1 = i
So our equation is y = x + 1
