Evaluate each expression if $x =\frac{3}{8},$ $y=\frac{4}{7}$ and $z=\frac{9}{10}$.
Your answer should be a reduced fraction or a mixed number with the faction part reduced (A mixed number can be entered in the form 2 3/4 to mean $2\frac{3}{4}$ ).

a) $x-y=\ \ $

b) $x+2y=\ \ $

c) $x+y+z=\ \ $