A = Pe^rt
Amount of interest paid = Principal*e^ (rate*time) 
(The rate must be in decimal form) 
3.15% / 100 = .0315
1,512 = P[e^(.0315*12)] 
1,512 / e^(.0315*12) = P
1036.06 = P
$1036.06 was the Principal 
** I left that value unrounded to the hundreds place because one doesn’t round with money. :) 
Good luck!