A local newsletter is printed on a printer with a cartridge that may break or run out of ink during operation. The cartridges can be replaced for $7.50, but if they fail when the newsletter is being printed, the cost is estimated to be $25 because of the delay in publication. The failure distribution of the cartridges is Weeks of Use Probability of Failure 1 .1 2 .2 3 .3 4 .4 Determine the optimal time to replace the cartridges.