A.T.Q, your equation would be:
x+y=15 (x=jar of small candy;y=of larger candy)----1
120x+80y=1560---------------------------------------------2
Sunstitute value of y from equation 1, which is y=15-x
120x+80(15-x)=1560
120x-80x+1200=1560
40x=360
x=9
So, 9 jars will contain small candies.