First find the marked price, then compare the selling price to find the discount.<br><br>&bull; Marked price (50% markup): \(\$800 \times 1.50 = \$1200\)<br>&bull; Discount = \(\$1200 - \$840 = \$360\)<br>&bull; Percentage discount = \(\frac{360}{1200} \times 100\% = 30\%\)<br><br>Final Answer: 30%