When is 20% off better than 20$ off
for what prices are x% off better than x$ off
for what prices are 20% off better than 30$ off

Price > 100$

Price > 150$

Step-by-step explanation:

Let us assume that x% off of price y$  is better than x$ off.

Hence,  

Hence, y > 100

Therefore, when the price is more than 100$, then only x% off on the price is better than x$. (Answer)

Again, assume that 20% off on price y$ is better than 30$ off.

Hence,

⇒ y > 150$

Therefore, when the price is more than 150$, then only 20% of on the price is better than 30$ off. (Answer)

ok then what happened.