Question 825682
Not too tough if you draw the trapezoid and label the sides according to your description.  


Not showing the figure, but stating expressions for each side:

Two non-parallel opposite sides, each x.
Short parallel side, x-4.
Long parallel side, x+5.


The perimeter is given as 18, so setup {{{x+x+(x-4)+(x+5)=18}}};
.
{{{2x+x-4+x+5=18}}}
{{{4x+1=18}}}
{{{4x=17}}}
{{{highlight_green(x=17/4)}}}, use this then to find each of the parallel side length.