Iwill mark you as brainlinest for correct

The question GIVES you the formula for any term:

                    a(n)  =  -16 + 2n

All you have to do is write the number of the term you want
in place of 'n' .

The 12th term is

                a(12) = -16 + 2(12)

                         =  -16 + 24

                         =      8       . 

Yes. there is a constant ratio of number of calories to gram of protein.12/3=24/4=32/8=44/11=4