${\left(\frac{a-b}{2}\right)}^2+{30}^2=c^2$

${\left(\frac{1}{3}d\right)}^2+{\left(\frac{2}{3}d\right)}^2=c^2\Rightarrow c=\frac{\sqrt{5}}{3}d$

$2\cdot {\left(\frac{1}{3}d\right)}^2=b^2\Rightarrow b=\frac{1}{3}\sqrt{2}d$