Answer: 
Price after discount: $21.25
Tip amount: $4.25
Explanation: 
We know the following information:
Original bill: $25 
Coupon: 15% off 
Tip: 20% after the discount is applied. 
Now, we first calculate the bill price after the discount. After a 15% discount, Karen needs to pay only 100% - 15% = 85% of the original amount and it is 

Hence we know that Karen has to pay $21.25 after the coupon is applied. 
Now we calculate the tip amount. 
The tip amount is 20% of the discounted price; therefore, 

Hence, we find that the tip amount is $4.25. 
To conclude, 
Price after discount: $21.25
Tip amount: $4.25