Question 851849
<pre>
The mid-segment of a trapezoid is the line segment connecting
the midpoints of the two non-parallel sides.  Its length is 
equal to the average of the length of the bases.  So

{{{(AB+DC)/2}}}{{{""=""}}}{{{MN}}}

{{{(8.2+DC)/2}}}{{{""=""}}}{{{9.5}}}

Multiply both sides by 2 to clear of fractions.

{{{8.2+DC}}}{{{""=""}}}{{{19}}}

Subtract 8.2 from both sides:

{{{DC}}}{{{""=""}}}{{{10.8}}}

Edwin</pre>