Write the equation to a line that goes through (3,15) and (7,21)

Y=mx + c

first find 'm'

m=y2-y1/x2-x1

m= 21-15/7-3

m=6/4 or 3/2

then substitute values in from either points

y=mx+c
15=3/2 * 3 + c
15=9/2 + c
15-9/2=c
11/5=c
therefore the equation must be y=3/2 x 11.5
note: you substitute with either (3,15) or (7,21) you will get the same answer either way.

One batch of muffins needs 2/3 of a cup.

12 * 2/3 = 8 cups. He needs 8 cups of milk for 12 batches of muffins. So he has enough milk.