How many marbles do you need to balance the scale?

When i add money am i supposed to make it like this 7+12 or 7.00+12.00 because i got 19 dollars for my answer

In which form is the following function written? y = - 2(x – 3)(x + 5)

Molly shared a spool of ribbon with 12 people. each person received 3 feet of ribbon. which equation can she use to find r, the number of feet of ribbon that her spool originally had?