A truck delivered *n* number of boxes weighing 20 pounds and *t* number of boxes weighing 30 pounds to a warehouse. The equation *w* = 20*n* + 30*t *can be used to determine the total weight *w*, in pounds, of the boxes. If the total weight of the boxes delivered was 480 pounds and 12 boxes weighed 30 pounds, how many boxes weighed 20 pounds?

**Maps to Category 15 of the book.**

**Answer posted on 08/01/2021**