To be able to determine which among the two coupons gives you a lower price, let's first determine the equivalent value of Coupon B's 30% off then we compared it if it is higher than Coupon A's $9 rebate or not. The higher the amount will give you a lower discounted price.
Let's determine the equivalent amount of Coupon B at 30% off.


Coupon B will give you $11.40 off on a $38 chair. Since $11.40 is higher than Coupon A's $9 dollar rebate, therefore, Coupon B will give you a lower price for the chair.
Let's determine the amount Coupon B will be lesser compared to Coupon A:


The price of coupon B is $2.40 lesser than coupon A.