J.R. S. answered 10/13/18
Ph.D. University Professor with 10+ years Tutoring Experience
Use the expression q = mC delta T
q = heat
m = mass
C = specific heat
delta T = change in temperature
q = (20.0 g)(1.80 cal/g/deg)(12 deg) = 432 cal
If you want the answer in joules, multiple by 4.186