if 255 g of water has 10.0 g of nacl dissolved into initially, how much nacl must be added in order to raise the mass percent of nacl by 10%?

Mass percentage is one way of representing the concentration of an element in a compound or a component in a mixture. To calculate percent by mass, you need to determine two things: the mass of just the element, and the molar mass of the whole compound. We calculate as follows:

.10 g NaCl / g NaCl + Water = ( 10.0 g NaCl + x ) / (10.0 g + 255 g + x )

x = 18.33 g NaCl needed

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current