Answer
\$13; \$8; \$10.50; \$2.50
Work Step by Step
When you split the difference the price is the average of the consumers willingness to pay and the suppliers willingness to accept.
$(13+8)\div2=21\div2=10.5$
The surplus is the same for both the consumer and the supplier.
$13-10.50=2.50$
$10.50-8=2.50$