Please help! I really don’t get this and it would be really helpful if you can give me the answers for these.

Answer:
for the first triangle, the length of the third side is 37 units
for the second triangle, the length of the third side is 29 units
Explanation:
Given the triangles in the attached image.
Let us apply the Pythagorean theorem to solve for the third side.
[tex]\begin{gathered} c^2=a^2+b^2 \\ c=\sqrt{a^2+b^2} \end{gathered}[/tex]For the first triangle;
[tex]\begin{gathered} a=12 \\ b=35 \end{gathered}[/tex]substituting the values;
[tex]\begin{gathered} c=\sqrt[]{12^2+35^2} \\ c=\sqrt[]{1369} \\ c=37 \end{gathered}[/tex]For the second triangle;
[tex]\begin{gathered} a=20 \\ b=21 \end{gathered}[/tex]substituting the values;
[tex]\begin{gathered} c=\sqrt[]{20^2+21^2} \\ c=\sqrt[]{841} \\ c=29 \end{gathered}[/tex]Therefore, for the first triangle, the length of the third side is 37 units
for the second triangle, the length of the third side is 29 units