Thank you for posting your question!
To solve this one you want to solve for the present value of both the $1 dividend and $20 selling price. Using the time value of money formula that would mean taking
$1 / (1 + 0.15) + $20 / (1 + 0.15)
=$0.87 + $17.39
=$18.26
So the current price of this stock would be $18.26