9. Foecke/McCarty's alternate theory regarding Titanic's demise revolved around the type of rivet used in the front one-fifth and back one-fifth of the ship. Unlike mid-ship, where steel rivets were used, the ends of the ship were secured with wrought iron rivets. Of the 18 wrought iron rivets obtained from the wreckage, 17 were missing heads (whereas only 2 of the 17 steel rivets were missing heads). The researchers suspected an overabundance of slag (the glassy byproduct of the iron manufacturing process) was to blame. Slag is known to improve wrought iron strength in concentrations up to 3% by mass, but concentrations higher than that will result in brittle wrought iron. Given a 5-lb iron rivet, what is the maximum mass of slag it could contain before becoming brittle? Give your answer in lb.