Let x represent the number of t-shirts you can buy.
The cost of one t-shirt is $11, and you have a coupon for $6 off, so each t-shirt will effectively cost $11 - $6 = $5.
You have $27 to spend, so the equation to represent the problem is:
$5x = $27
To solve for x, divide both sides of the equation by $5:
x = $27 / $5
x = 5.4
Since you can only buy whole t-shirts, you can buy a maximum of 5 t-shirts using your coupon and money.