The answer is 670.
this is because 96 plus 287 is 383.
so he sold 287 on the 1st day, and 383 on the second day.
383 plus 287 equals 670.
By using pythagoras theorem where
(Base)^2 +(perpedicular)^2 = (hypotenuse)^2
So,
(5)^2 +(12)^2 = (hypotenuse)^2
25 + 144 = (hypotenuse)^2
169 = (hypotenuse)^2
13 = hypotenuse
So, hypotenuse = 13