I don't understand this can someone plz help

Bob is putting books on a shelf and takes a break after filling 18 1/2 inches on the book shelf. the book shelf is now 2/3 full. how long is the entire bookshelf?

If 1.4% of the mass of a human body is calcium, how many kilograms of calcium are there in a 165-pound man? 1.0 kg ca 5.1 kg ca 1.0 x 102 kg ca 5.1 x 102 kg ca

The management of a supermarket wants to adopt a new promotional policy of giving a free gift to every customer who spends more than a certain amount per visit at this supermarket. the expectation of the management is that after this promotional policy is advertised, the expenditures for all customers at this supermarket will be normally distributed with a mean of $95 and a standard deviation of $20. if the management wants to give free gifts to at most 10% of the customers, what should the amount be above which a customer would receive a free gift?