Question 150866
Use the Pythagorean theorem

You are being asked for the length of the diagonal between two opposing corners
{{{c^2 = a^2 + b^2}}}
{{{c^2 = 4^2 + 8^2}}}
{{{c^2 = 16 + 64}}}
{{{c^2 = 80}}}
{{{c = 8.94}}}

Answer D

As far as the sketch goes, make a rectangle that is twice as long as it is wide. Label the short side 4 and then long side 8. Then draw a diagonal line from the top left to the bottom right corners. The result should look like a "backslash in a box"