Ok so, 5 pounds is 12$, since we can't count by 5's to get our answer we can divide 12 by 5 to see how much one pound would cost.
12 / 5 = 2.4
One pound of broccoli costs $2.40, SO. To find how much 7 pounds would cost we multiply 7 by 2.4.
7 x 2.4 = 16.8
So, 7 pounds of broccoli costs $16.80