Answer:
x = 14
Step-by-step explanation:
Since ABCD is an isosceles trapezoid, we know that AC = BD
Therefore:
x= 3x - 28
Now we can just solve the equation for x:
x - x = 3x - x - 28
0 = 2x - 28
0 + 28 = 2x - 28 + 28
28 = 2x
28/2 = 2x/x
14 = x
x = 14
Hope this helped!
