Answer:
390 pens in total
Step-by-step explanation:
Each box has 6 black and 4 black
so the total amount of pens per box should be 10 because 6+4=10
Since we have to use distributive property you can write the equation (6+4)*39 because you need to figure out the total amount of pens in all the boxes.
6+4 is 10
and 10 * 39 is 390
therefore the answer is 390 pens in total