Answer:
the price of the bagel is 1.5 $
and a cup of coffee is 3.5 $
Explanation:
6c+12b=39
2c+3b=11.5 |*(-3)
6c+12b=39
-6c-9b=-34.5
---------------------
 / 3b=4.5
so the price of the bagel is 4.5/3=1.5 $
then 2c+3*1.5=11.5
 2c+4.5=11.5
 -4.5 -4.5
 2c=7 $
 and a cup of coffee is 7/2=3.5 $