Anytime a GRE problem has variables in the choices, as this one does, consider plugging in your own easy values and modeling the equation as an effective and efficient alternative to manually translating the algebra. Often times an easy total number can be created by simply multiplying all numbers in a problem, since you know that any requisite division will then result in whole numbers.

As always, skip to the end of the problem to ID what value is being sought. In this case, we seek how many more dollars it will cost per person.

Now, work through the steps of the problem with the plugging in tactic that we've already identified as a possible approach. According to the problem it costs $x to rent a boat and rather than 20 people, now 12 people will be splitting the cost. Multiply 12 x 20 = 240 and use that value for the cost of the boat or x.

Then, determine the cost per person if there were 20 people by taking the cost and dividing that by the presumed number of people. So, 240 ÷ 20 = $12 per person.

Next, determine the cost per person now with 12 people. So, 240 ÷ 12 = $20 per person.

Finally, determine the number of dollars per person more by finding the difference between these two values or 20 - 12 = $8.

Now, test the choices using the value of 240 for x while seeking a choice to match our target difference of $8.

A. x/8 --> 240 ÷ 8 = 30 | Eliminate

B. x/12 --> 240 ÷ 12 = 20 | Eliminate

C. x/16 --> 240 ÷ 16 = 15 | Eliminate

D. x/20 --> 240 ÷ 20 = 12 | Eliminate

E. x/30 --> 240 ÷ 30 = 8 | Correct!