Answer
$A=0.249kg$
$C=0.194kg$
$D=0.0553kg$
Work Step by Step
$(30cm)(A)=(7.50cm)(D+C+B)$
$(5.0cm)(B)=(15.0cm)(D+C)$
$(17.5cm)(D)=(5.0cm)(C)$
$(D+C)=0.249kg$
$D=\frac{(5.0cm)(C)}{17.5cm}$
$\frac{(5.0cm)(C)}{17.5cm}+C=0.249kg$
$C=0.194kg$
$D=0.0553kg$
$A=\frac{(7.50cm)(0.249kg+0.748kg)}{30cm}=0.249kg$