Yogen no Keizaigaku

The Oracle Princess Alfina suddenly announces an ominous prophecy to the people of the Kingdom of Crownheight. However, shunned as she is for being a descendant of rebel blood, her words are heeded by no one. On the other hand, Ricardo, the adopted heir of a peddler, who also happens to be an economics department graduate reincarnated into this world, attends the Royal Academy to study as a merchant. During an argument with a much more affluent merchant, the one to stick up for him is none other than Alfina. As the distance between them rapidly closes, Ricardo makes full use of his modern knowledge of science, mathematics and economics to stand against the unknown disaster of prophecy!

(Source: J-Novel Club)