Solve proportion S/84=3/21

For the rule of 78, for a 12-month period, the last term in the sequence is 12 and the series sums to 78. for an 10 month period, the last term is and the series sum is . for a 15 month period, the last term is and the series sum is . for a 20 month period, the last term is and the series sum is

Asap! i'm not good math and i'm lost.

The paint recipe also calls for 1/4 cup of food coloring. tyler says mrs. mcglashan will also need 6 cups of food coloring. do u agree or disagree? explain.