Answer:
67
Step-by-step explanation:
Since the diagonals in a rectangle are congruent, AC=BD and
7x+18=10x-3
We need to separate x -- to do that, we can first subtract 7x from both sides, resulting in
18=3x-3
Next, add 3 to both sides to get
21=3x
Divide both sides by 3 to get
x=7
Then, we just plug x into 10x-3 to get BD = 7*10-3 = 67
