$60
Step-by-step explanation:
The unit rate can be determined by dividing $24 by 8 attendees to get
[tex]\dfrac{\$24}{8\:\text{attendees}} = \$3/\text{attendee}[/tex]
so when 20 people are attending the graduation picnic, his total cost is going to be
[tex]20\:\text{attendees}×\dfrac{\$3}{\text{attendee}} = \$60[/tex]
