I need a explanation plz. Doesn't have to be perfect.

They arrive at the same answer because Jenna used the distributive property while Mia used the order of operations PEMDAS. In a lot of aspects of math, there are many approaches to reach the same answer.

Jenna's approach makes more sense, in my opinion, because when we multiply large numbers we're going to use the distributive property anyway. So why not just have it written down instead of done mentally in our head.

As a visual way to see why this works, check out the diagram below. We have a rectangle with height 5. The length of 34 is broken up into 30 and 4, so 34 = 30+4.

The blue portion has area of 5*30 = 150, while the red portion has area of 5*4 = 20. The two regions combine to 150+20 = 170.

So this diagram shows why Jenna's method is valid. Mia's method is valid as well, but again, we'll use some form of the distributive property to multiply 5 and 34. The only advantage that Mia has is that she uses one less written step compared to Jenna.