Answer:
[tex]\left\{\begin{array}{l}x+y\ge 20\\ \\10x+20y\le 280\end{array} \right.[/tex]
Step-by-step explanation:
Let x be the number of $10 tickets the radio station gives away and y is the number of $20 tickets which the radio station gives away.
Number of tickets:
At least 20, so
[tex]x+y\ge 20[/tex]
Cost:
x tickets for $10 each cost $10x
y tickets for $20 each cost $20y
Total cost:
$(10x+20y)
The total cost of all the tickets they give away can be no more than $280, so
[tex]10x+20y\le 280[/tex]
We get the system of two inequalities:
[tex]\left\{\begin{array}{l}x+y\ge 20\\ \\10x+20y\le 280\end{array} \right.[/tex]
