The club needs to make and sell 29 t-shirts in order to profit at least 150.
Step-by-step explanation
Suppose , the number of t-shirts the club needs to make and sell is

Selling price of each t-shirt is 15, so the total selling price of
t-shirts

It costs 20 plus 9 per t-shirt to make the t-shirts. So, the total making cost of
t-shirts

Now for getting profit at least 150 , the equation will be.....

It means the value of x should be at least 28.333...
As here x is the number of t-shirts and it can't be in decimal , so the minimum value of x will be 29.