Hey there!
Answer: 400 k-cal
I remember learning that 4,000 k-cal would be approximately 40 k-cal for the primary consumers, which, that would be how much would be available. Now, if we would want for the primary consumers to consume more k-cal, it's obvious that there would then have to be more k-cal from the producers level of the ecosystem.
Formula of k-calories: k-cal÷20(4)= k-cal = k-cal × 2 = k-cal
As we plug in this formula into our problem above, our answer would be explained below.
40,000 ÷ 20 = 2,000 × 2 = 4,000 ÷ 100 = 400 k-cal
Answer: 400 k-cal