Answer: The required value of a is 8.
Step-by-step explanation: Given that the perimeter of the trapezoid shown is 284 units.
We are to find the value of a.
From the figure, we note that
the lengths of the sides of the trapezoid are 12a, 6a+8, 10a-4 and 6a+8.
We know that
the perimeter of any polygon is equal to the sum of the lengths of the sides of the polygon.
Therefore, for the given trapezoid, we must have
![12a+6a+8+10a-4+6a+8=284\\\\\Rightarrow 34a+12=284\\\\\Rightarrow 34a=284-12\\\\\Rightarrow 34a=272\\\\\Rightarrow a=(272)/(34)\\\\\Rightarrow a=8.](https://img.qammunity.org/2020/formulas/mathematics/middle-school/is7mw3kwmyicswvkwjxdmt6qr99eilekfa.png)
Thus, the required value of a is 8.