Iwas wondering if you could check my work.

I would say the correct answer is 1728.

The figures are increasing by half each week. To calculate the figure for the 11th week you could use this sum: 20×1.5^11
20 is the starting figure. 1.5 is the multiplying factor to get the figure for the next week and the 11 is the number of weeks.

I hope this helps.