It takes joey one-sixteenth of an hour to write one you card how many cards can he write in three fourth of an hour

You want the two fractions of an hour's denominators to match. So we have to convert three-fourths of an hour to sixteenths:

3/4 * 4/4 = 12/16

So, since he's writing for twelve sixteenths of an hour,  you multiply how many he can write in one hour by twelve:

1 card per 1/16 of an hour * 12 sixteenths of an hour =
12 cards per 12/16 hour 

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