Answer :
[tex]Calculating\ first\ 15\%\ sale:\\\\
15\%*D=0,15*D=0,15D\\New\ price:\ \ \D-0,15D=0,75D \\\\Sale\ for\ staff:\\\\
10\%(0,75D)=0,1*0,75D=0,075D\\\\New\ price:\ \ \ 0,75D-0,075D=0,675D\\\\Staff\ will\ pay\ 0,675D\ for\ this\ dress.[/tex]