Answer: He bought 8 t-shirts
Step-by-step explanation:
Set up a proportional relationship
If t-shirts equals to $13, then how many t-shirts will equal to $20.80, we will represent that number of t-shirts by the variable x.
[tex]\frac{5}{x} = \frac{13}{20.80}[/tex]
13x = 104
x = 8