There are 12 feet of wrapping paper on each roll. jill needs 84 feet of wrapping paper. which equation can jill use to find the number of rolls, r , she needs? need equation

Let
r > number of rolls
x> feet of wrapping paper needs

we know that 
1 r > 12 feet of wrapping paper
therefore
r=(1/12)*x > equation required

for x=84 feet of wrapping paper
r=(1/12)*84=7 rolls