Lemme have a go at this.
20% of a number is 1/5 of the number
So we can do 1/5x50=10. So she has to pay $10 per delivery
(Btw that was the example that the problem gave I think)
Now we can use that mothod for all the prices
RIght now we are looking for emilies profit.
(Sorry that I didnt add the dollar sign I thought it would be confusing)
Now lets add them up
We will get $69.60 excluding the tip
Now we add the tip to it.
The total tip is $21
Now we add $21+69.60