Answer:
BD=4
Step-by-step explanation:
Since AB and CD are congruent (or the same length) we can equal the corresponding equations for the two:
2x+5x+7=5x+7+3x-4
(simplify)
7x+7=8x+3
(get variables to one side)
7x+7-8x=3
7x-8x=3-7
(simplify)
-x=-4
(multiply by -1 to get x by itself)
x=4
Now, plug x=4 into the BD equation (3x-4)...
3(4)-4=BD
12-4=BD
8=BD
