$1.29 for 20 ounces

Unit rate!

To find the "Unit rate" you need to find the price for one ounce.  So, you need to divide 1.29 by 20.

When you do this you get the following decimal

0.0645

Since we are talking about money, we are often expected to round to the nearest cent.  So the cost-per-unit is $.06

if you was gonna solve for a, a is a   < -12