Question 151109
We know that a parallelogram has 2 opposite sides with EQUAL lengths and 2 opposite bases also with equal lengths.
To find the opposite sides with given,
{{{3x+20}}} -------> A
{{{5x-8}}} --------> B
In B we get the value of "x" ---> {{{x=8/5}}} 
Then substitute this in A, 
= {{{(3)(8/5)+20}}}
= {{{(24/5)+20}}}
= {{{(24+100)/5}}}
= {{{124/5}}} ----------> {{{24.8}}}, Length of each side
Thank you,
Jojo