ANSWER:
[tex]\begin{gathered} d_1=4 \\ d_2=5 \end{gathered}[/tex]STEP-BY-STEP EXPLANATION:
We have the following expression
[tex]d^2-9d+20=0[/tex]Solving fir factoring:
[tex]\begin{gathered} d^2-4d-5d+20=0 \\ d(d-4)-5(d-4)=0 \\ (d-4)\cdot(d-5)=0 \\ d-4=0\rightarrow d_1=4 \\ d-5=0\rightarrow d_2=5 \end{gathered}[/tex]