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You now have the answer as to how to approach the question.
However, it is worth including a comment as to the question's interest in a 6% climb gradient.
You will be aware that CAO 20.7.4.7 restates the now defunct CAO 101.22 certification requirement that a light aircraft has to be able to achieve a takeoff WAT limit climb not less than 6%. This is to prevent takeoffs at excessive weights where the climb gradient capability is a bit too low for comfort.
What this meant under 101.22 was, and for 20.7.4, is, that, if an aircraft at higher weights (and, typically, higher altitudes and OAT) could not make 6% at the take off safety speed, then the takeoff chart had to have some subsidiary data to restrict the takeoff weight so that the 6% could be achieved. Many light aircraft are never WAT-limited.
If you refer to the exam booklet at the Fig 3 takeoff chart (in the old DCA P-chart format) you will see that there is a climb weight limit shown in the density height grid in the lower left hand corner. The take off chart at Fig 5 shows an alternative presentation with a climb limit.
If you have a look at the Echo takeoff chart, you will see that there is NO climb limit included. What this means is that the Echo, for any takeoff within the conditions of the takeoff chart, will ALWAYS see MORE THAN 6% at the takeoff safety speed.
You will see questions, such as the one you have cited in this thread, where the thrust of the question is to find a ROC to achieve 6% for the Echo at the takeoff safety speed and takeoff power. Now, if you are always going to see MORE than 6% under those conditions then, unless the question says something like "minimum ROC" it is a bit meaningless. To achieve 6% for the Echo on takeoff, you would have to reduce the power setting.
Such questions are a bit silly but you will need to answer them in the manner sought by the the examiner. Just keep in mind that, should you be in a non-WAT limited aircraft, and you see a ROC relevant to 6%, then something is not quite right for the takeoff.
Engineering specialist in aircraft performance and weight control.
