For a complete understanding of the question please find the diagram in the file attached.
In the diagram a perpendicular DP is dropped from D on AB as shown.
It is given that
and that
. Thus, the
. This is because we know that the interior angles of any triangle add up to make
.
Thus,
gives:



Thus, PB=CB-CP=15-5=10
Now, since,
, then by corresponding angles, 
Also, we note that DE=PB=10
Thus, in
,



Thus, now to find the area of the triangle
all that we have to do is use the Area formula as:
Area=
x base x height =
square units