Answer:
The marked up percentage is 112.5%
Step-by-step explanation:
The cost price of the emerald pendant = $400
The selling price of the emerald pendant = $840
Now, the Mark up Price = Selling Price - Cost Price
= $840 - $400 = $450
Also, 
= 
⇒ Percentage of Mark up Price = 112.5%
Hence, the marked up percentage is 112.5%