Final answer:
To determine the unit rate of $90 for 3 video games, divide the total cost by the number of games, yielding the rate of $30 per video game.
Step-by-step explanation:
To write the ratio $90 to rent 3 video games as a unit rate, one must divide the total cost by the number of video games. Hence, $90 divided by 3 video games gives us a unit rate cost per video game. Performing this calculation, $90 ÷ 3 = $30 per video game.
The correct unit rate is therefore $30 per video game, which means the answer is a. $30 per video game.