Answer
9 curtains
Work Step by Step
You have 4 yards and you have to change them to inches.
Since 1 yard=36 inches, so 4(36)=144.
We know that 16 inches of fabric is used by each curtain. We have 144 inches of fabric so 144$\div$16=9 curtains.
Thus, you could make 9 curtains with 144 inches of fabric.