Answer:
The value of a is 14 unit and the value of b is 
 unit
 unit 
Step-by-step explanation:
Draw a perpendicular line from vertex B to DC at E.
Labeling the diagram as shown in the attachment: 
Now, as you can see from the Figure as shown in the attachment that 
 represents the rectangle because a rectangle is a quadrilateral with four right angles and their opposite sides would be parallel.
 represents the rectangle because a rectangle is a quadrilateral with four right angles and their opposite sides would be parallel.
Therefore, we have the sides 
 unit , and
 unit , and 
 unit.
 unit.
Consider the right triangle BEC
BY 45 45 90 triangle is a special type of isosceles right triangle where the two legs are congruent to one another and the non-right angles are both equal to 45 degrees. 
therefore, the length of side, 
 unit
 unit
Using trigonometric ratio; to find the value of b:

∴ using trigonometric sine ratio in triangle BEC, we have
 or
 or
 
 
On Simplify:
 unit
 unit
and the value of a = DC = DE+EC=8+6=14 unit
Therefore, the value of a is 14 unit and b is 
 unit
 unit