From what the statement mentions we know that
To solve the exercise, you can first find how many people there are per square mile in Rhode Island, using the rule of three:


Then, in Rhode Island, there are 1000 people per square mile.
Now, you can find the population of Alaska if there were the same number of people per square mile as in Rhode Island, again using the rule of three:


Therefore, if Alaska had the same number of people per square mile as Rhode Island, its population would be 663 million people.