Final answer:
The correct equation to find the amount Shelly still owes her dad is x + 17 = 20. By subtracting 17 from both sides, we find that x, the amount still owed, is $3.
Step-by-step explanation:
To find x, the amount Shelly still owes her dad, we can set up an equation that represents the total amount borrowed and the amount that has been paid back. Shelly borrowed $20, and has paid back $17. This situation can be described by the equation x + 17 = 20. To solve for x, we need to find out how much more she needs to pay to reach the total of $20 that she borrowed. So we can subtract 17 from both sides of the equation to isolate x:
x + 17 = 20
x = 20 - 17
x = 3
Therefore, Shelly still owes her dad $3.