Answer:
Julie will have $12 on the 6th day not after the 6th day.
Explanation:
Given
Day 1: $6
Required
Matt's error
First, I'll assume that Julie keeps $2 everyday.
So on the 6th day, the amount Julie will have is calculated as follows.
Amount = 6 * $2
Amount = $12
Hence, Julie will have $12 on the 6th day, not after the 6th day as Matt implies and this is what Matt is doing wrong.