a,
\(Vr=\frac{200}{0,8}=250\left(ml\right)\)
\(V_{dd}=250+750=1000\left(ml\right)\)
\(Dr=\frac{Vr}{V_{dd}}.100=\frac{250}{1000}.100=25\)
b,
\(Vr=\frac{2000.25}{100}=500\left(ml\right)\)
\(V_{dd}=2000+500=2500\left(ml\right)\)
\(Dr=\frac{Vr}{V_{dd}}.100=\frac{500}{2500}.100=20\)