Answer:
a = 16
Step-by-step explanation:
Look at the picture.
The formula of an area of a trapezoid is:
[tex]A=\dfrac{b_1+b_2}{2}\cdot h[/tex]
[tex]b_1,\ b_2[/tex] - bases
[tex]h[/tex] - height
We have:
[tex]A=128,\ b_1=a+2,\ b_2=a-2,\ h=8[/tex]
Substitute:
[tex]128=\dfrac{a+2+a-2}{2}\cdot8\\\\128=\dfrac{2a}{2}\cdot8[/tex]
[tex]128=8a[/tex] divide both sides by 8
[tex]16=a\to a=16[/tex]
