This is a sigma question and basically every Monday is calculated by 500 + 10(x-1) where x is the week.

I was a bit lazy so I used a sigma calculator this time around and at x=101, you now had a number greater than 100,000.

Work-wise I put done how I would do it.
Sigma(490)+Sigma(10x) = 100,000 then solve for x but I am a bit lazy.