a ruler is used for measuring the length of an object & a backpacks is a mean of preposition ->  a ruler can be used for measuring the length of a seashell  a balance is used for measuring the mass of an object & a seashell is a kind of object -> a slip is used for systems the want of a close a balance is used for measuring the mass of a seashell  a ruler can be used for measuring the length of a seashell & a slip is used for systems the want of a close -> a ruler and balance can be used to measure the length and mass of a seashell